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Interview Preparation Material for Testing consultants MS-BUIT OASIS Onsite
Description of Change FAQs FAQs and and read readin ing g mater ateria iall for for Testers. Updat pdated ed with ith more more FAQ FAQs on on Test esting ing and some answers for existing ones.
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1. Intr Introd oduc ucti tion on
The purpose of this Guide is to help our consultants (Testers) succeed in Microsoft Redmond Interviews. This document covers most of the interview questions in various topics such as Testing, SQL Server, data warehouse, and basic .NET concepts. Also reading material included for the above mentioned areas.
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2. Questions 2.1. 2.1.
Test Te stin ing g int inter ervi view ew Qu Ques esti tion onss
Following list include questions for Tester as well for Test Lead. Interviewer eva luates the candidate’s real time experience and in-depth knowledge of testing process. Answers are not given for some of o f the questions. 1.
What is a Test plan
A Test Plan is a detailed plan for testing, c overing the scope of testing, the methodology to be used, the tasks to be performed, resources, schedules, risks, and dependencies. A Test Plan is developed prior to the implementation of a project to provide a well defined and understood project roadmap. A Test Specification defines exactly what tests will be performed and what their scope and objectives will be. A Test Specification is produced as the first step in implementing a Test Plan, prior to the onset of manual testing and/or automated test suite development. It provides a repeatable, comprehensive definition of a testing campaign 2. Wh What at is a Tes Testt Cas Casee
A test case is a document that describes input, action, or event and an expected response, to determine if a feature of an application is working correctly. co rrectly. The process of developing test cases can help find problems in the requirements or design of an application, since it requires completely thinking through the operation of the application. 3. Qual Qualiti ities es of of a good good tester tester A good test engineer has a 'test to break' attitude, an ability to take the point of view of the customer, a strong desire for quality, and an attention to detail. Tact and diplomacy are useful in maintaining a cooperative relationship with developers and an ability to communicate with both technical (developers) and non-technical (customers, management) people are useful. Previous software development experience can be helpful as it provides a deeper understanding of the software development process, gives the tester an appreciation for the developers' point of view, and reduce the learning curve in automated test tool programming. Judgment skills are needed to assess high-risk areas of an application on which to focus testing efforts when time is limited. 4. Possible Test plans/ Test cases for Yahoo Messenger Convincing a developer about a bug 5. Have u written any test scripts in WinRunner. 6. How many many types types of recording recording modes modes in winrunner winrunner and what are they they
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1.Context Sensitive: Records your Operations in terms of GUI Object in your application. WinRunner identifes each object you click (window, menu, list or button), and the type of operation you perform (press, enable, move or select). 2. Analog: WinRunner records the exact co-ordinates travelled by the mouse, as well as mouse clicks and keyboard inputs. Choose Context Sensitive mode if: a. The Application contains GUI objects. b. Exact mouse movements are not required. c. Plan to reuse the test in different versions of the application. Choose Analog mode if: a. The Application contains bitmap areas. b. Exact mouse movements are required. 7. What are the check points in winrunner and Types of check points
Checkpoints allow you to compare the current behavior of the application being tested to its behavior in an earlier version. GUI Checkpoints verify information about GUI obects. Bitmap Checkpoints take a "snapshot" of a window or area of application and compare this to an image captured in an earlier version. Text Checkpoints read text in GUI objects and in bitmaps and enable you to verify their contents. Database Checkpoints check the contents and number of rows and columns of a result set, which is based on a query you create on your database. 8. What is TSL
When you record a test, a test script is generated in Mecury Interactive's Test Script Language. Each TSL statement in the test script represents keboard and/or mouse input to the application being tested. TSL is a C-like programming language designed for creating test scripts. It combines functions developed specifically for testing with general purpose programming language features such as variables, con trol-flow statements, arrays and user defined functions. You can enhance a recorded test script simply by typing programming elements into the test window. 9. What is System testing and integration testing
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System testing - black box type testing that is based on overall requirement specifications; covers all combined parts of a system. Integration testing - An integration test verifies that all the parts of an application "Integrate" together or work as expected together. This is important because after all the units are tested individually we need to ensure that they are tested progressively. 10. Have u done Integration testing.? 11. Who will do integration testing, is it tester or developer? 12. What is the BVA (Boundary Value Analysis)? 13. What is the Equivalence partitioning testing? 14. Have u done components testing if yes how is the process? 15. What is regression testing
Regression testing is re-testing after fixes or modifications of the software or its environment. The selective retesting of a software system that has been modified, to ensure that any bugs have been fixed and that no other previously working functions have failed as a result of the modification and that newly added features have not created problems with previous versions of the software. 16. How do u write test cases 17. What are the testing techniques used for writing the test cases. 18. Have u done any programming. 19. If their r four modules A, B, C, D, development of each module takes 1 month time then how do u plan integration testing. 20. Tell some 5 function names in Winrunner
Function Categories - Analog functions, Context-sensitive functions, customization function and Standard Functions. Analog functions - check_window (compares bitmap of an AUT window to an expected bitmap) click, click_on_text, dbl_click, get_x, get_y, wait_window Context Sensitive - obj_check_bitmap, win_check_bitmap, button_press, button_set, button_check_info, button_check_state, db_check, db_connect, db_disconnect, db_execute_query, db_get_field_value 21. As u said that u r leading a team of 2 members how will u motivate the team point out their plus points, even if they fail to commit activities. Tell them how to meet commitments in future. keep monitor them, analyze, give feedback. 22. If u are to do regression testing for n number of times, do u think doing the same work is a boring?
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23. What is difference between user requirements and functional specification The Functional Specification is created after the Software Requirements Document. It provides more detail on selected items originally described in the Software Requirements Document. The Functional Specification describes the features of the software product. 24. What are different testing methodologies? 25. How will you test a telephone set 26. How do you plan testing for a .Net project? 27. How did u manage testing in previous applications? 28. What is test estimation? 29. What are the possible criteria's for testing an Indian ATM machine? 30. How do you test an Remote control How long would you take to test it 31. What is Business requirement and How is different from functional specification 32. How do you do estimates for a test plan? 33. How do you prepare an effort plan? 34. What is software validation matrix? 35. What is traceability matrix? 36. What is negative testing and what is a boundary testing? 37. What is com and how is it different from business logic? 38. What’s cyclomatic matrix? 39. what’s CMM / why (Accenture become CMM level 5 by dec 25) - what's kpa, level 40. What’s v- model? 41. How'll u test a coffee machine?? 42. How can it be known when to stop testing? Common factors in deciding when to stop testing are: Deadlines (release deadlines, testing deadlines, etc.) • Test cases completed with certain percentage passed • Coverage of code/functionality/requirements reaches a specified point • Bug rate falls below a certain level. • 43. What if there isn't enough time for thorough testing? ( If there is only week of testing time is given for testing team how will u come up with task of completing complete testing.) Considerations can include: Which functionality is most important to the project's intended purpose? • Which functionality is most visible to the user? • Which functionality has the largest safety impact? • Which parts of the code are most complex, and thus most subject to errors? • What do the developers think are the highest-risk aspects of the application? • 44. What is parameterization in load testing? 45. What is the content of a BRS(Business Requirement Specification)? 46. Who will prepare Design specs and functional specs? 47. When we r integrating two modules what testing we will do retesting or regression?? 48. Write few sample test cases for integration testing?
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49. Consider a page contains 10 links at the recording time and in the execution time there are 20 links. (Take the example of a Search page) How will u handle the situation in WR? 50. If only one module is available and the second module is not ready then how will u do functional testing of the first module? 51. There is a text box and a submit button. If you enter "sp_who" in the text box and press enter what happens?? If an error occurs why it will occur and what makes it to go wrong. And what type of testing u calls it as?? 52. What is harness testing? 53. What is V model and explain various stages 54. Bug life cycle? 55. Explain about your recent project? 56. How do u do database check point in WR? 57. Ever written any code in WR or recorded it? 58. Explain Data driven Test. Explain the code in it. 59. The project needs Visual Tester, but u doesn't know it. Can u manage it? 60. If I give you an option of selecting Front end and Back end testing which one you will take and why? 61. What is primary key? And what r the differences between primary and unique key? 62. What are indexes? And how many types of indexes are there? 63. There is a table with 10 columns and I want to put 10 clustered indexes on it. Is it possible? 64. Same Question as above but with one clustered and 9 non clustered indexes. Is it possible? 65. There are 50 columns in a table. Write a query to get first 25 columns 66. What is the difference between Quality Assurance (QA) & Quality Control (QC) 67. Discussion on BVA (Boundary Value Analysis) and other techniques 68. Methodologies adopted for writing test cases 69. How do we test a calculator and an ATM system 70. What is a good bug? 71. Who is a good tester? 72. what is the best bug that u found out 73. Given a web application. What are the various testing scenarios and difference with client server application? What will u test for in these scenarios? 74. What is your achievement in testing? 75. What are the different tests in system test? 76. What is load and stress testing? 77. What is ad hoc testing? 78. What is monkey testing, exploratory testing, unit testing, smoke testing? 79. What is severity and priority and how would u c lassify severity in bugs. 80. Discussion on BVA (Boundary value analysis) and equivalence partitioning 81. What was your worst project & what was the b est in your career till now? 82. How did you manage your last project? 83. Have you done performance testing? Explain.
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84. How do you troubleshoot when 404 err occurs while trying to access a website application? 85. Dev is unable to repro the bug. What would you do? 86. How do you log a bug in the product studio? Ans: Bug Description, Title, Reprosteps, expected result, actual results, defect screen shots etc. 87. How do you set severity of a bug? Ans: explain different severity levels 88. What would you test when a new column is added in a table and there is a view already exists on that table? 89. How do you validate data that is moved from a source server to destination server? Write the queries if any? 90. Describe yourself and your job experience? Ans: give more info about your job experience and roles & responsibilities. 91. Explain your previous project architecture? 92. What is a Triage meeting? What is the need of it and who all participate in it? Who drives it? Ans: Triage meeting will be driven by Test Lead to primarily discuss the priority level of the bug resolution. Mandatory participants would be Test lead, Dev Lead, Business analyst, Program manager. 93. How do you test a Web service? 94. Where do you check event log? 95. What are all different categories of test cases for testing a website like hotmail.com? 96. What is performance testing? Give an example 97. Why do you think we should give you this job? 98. Write test cases for a word application over web. It is a scenario that the word application is available over web and users can subscribe it for a day or month or a year and so on. You have to write test cases to test this feature. 99. Explain SDLC process and what would be the test involvement at each phase? 100. You are a test lead and you have all the test cases and scripts ready to test a software. Required time for test pass is five days and your Dev manager wants to complete the test pass in 3 days. How do you handle this situation? 101. What is Localization testing? How do you perform it? 102. Explain SDLC process as per x-BUIT standards? And w hat is the exit criteria in each phase? 103. How do you install a build/drop in test environment? Ans: Test expects a build/drop installation notes with the release and build en gineer or QA team would install the drop based on the install notes provided. 104. How do you perform test estimation for a project?
2.2.
.NET and C# questions
Sometimes there are requirements where the candidate should have both development as well as test experience. Having basic knowledge is sufficient to get thru. 1.
Write the code to Concatenate two strings, remove a word from a string etc.
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2. write a function to find distance between two points? (Ans: Square root of (a2 + b2)) 3. Write code or algorithm to check a point in a rectangle. 4. Algorithm to find out a duplicate element in a integer array containing 1001 elements without accessing the array variable more than once. 5. What is difference between Const & ReadOnly keywords? 6. What you do and don't like with C# language? 7. How do you load xml from an xml file into a Dataset? 8. What is .Net frame work all about It’s a framework with some standards. So that all applications which written with .net can run virtually any machine / os/ hardware which supports .net framework. its o/s indepenedent/ language independent/ vendor independent. A dll we wrote in C# can be accessible with VB.NET 9. Winforms: what are different methods you have in a mouse event? 10. write a function in C# for Anagrams check. Ex: str1= DEAL, Str2=LEAD – Pass Str1=SALESMAN, str2=SALESMEN – fail 11. What is .NET? 12. What is MSIL? 13. What is CLR? 14. What is CLS? 15. What is CTS? 16. What is assembly? Difference between shared assembly and private assembly? 17. What is application domain? 18. What is Reflection? 19. What is a manifest? 20. Difference between managed code and unmanaged code? 21. What is the use of VS.NET? 2.3.
MS SQL Server interview questions
This is a set of more than a hundred Microsoft Testing interview questions. Testers are expected to have good knowledge in SQL Server. Some questions listed below are open-ended, and some of them do not have answer. 1. What is normalization? - Well a relational database is basically composed of tables that contain related data. So the Process of organizing this data into tables is actually referred to as normalization. 2. What is a Stored Procedure? - Its nothing but a set of T-SQL statements combined to perform a single task of several tasks. It’s basically like a Macro so when you invoke the Stored procedure, you actually run a set of statements. 3. Can you give an example of Stored Procedure? - sp_helpdb , sp_who2, sp_renamedb are a set of system defined stored procedu res. We can also have user defined stored procedures which can be called in similar way.
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4. What is a trigger? - Triggers are basically used to implement business rules. Triggers is also similar to stored procedures. The difference is that it can be activated when data is added or edited or deleted from a table in a database. 5. What is a view? - If we have several tables in a db and we want to view only specific columns from specific tables we can go for views. It would also suffice the needs of security some times allowing specific users to see o nly specific columns based on the permission that we can configure on the view. Views also reduce the effort that is required for writing queries to access specific columns every time. 6. What is an Index? - When queries are run against a db, an index on that db basically helps in the way the data is sorted to process the query for faster and data retrievals are much faster when we have an index. 7. What are the types of indexes available with SQL Server? - There are basically two types of indexes that we use with the SQL Server . Clustered and the NonClustered. 8. What is the basic difference between clustered and a non-clustered index? - The difference is that, Clustered index is unique for any given table and we can have only one clustered index on a table. The leaf level of a clustered index is the actual data and the data is resorted in case of clustered index. Whereas in case of non-clustered index the leaf level is actually a pointer to the data in rows so we can have as many non-clustered indexes as we can on the db. 9. What are cursors? - Well cursors help us to do an operation on a set of data that we retrieve by commands such as Select columns from table. For example : If we have duplicate records in a table we can remove it by declaring a cursor which would check the records during retrieval one by one and remove rows which have duplicate values. 10. There is an Employee table (fields: empID, Address, Name) and Salary table (fields: empID, salary). Write a query to retrieve the employee address and salary of all employees. 11. How do you validate data that is moved from a source server to destination server? Write the queries if any? 12. Can you tell me the difference between DELETE & TRUNCATE commands? Delete command removes the rows from a table based on the condition that we provide with a WHERE clause. Truncate will actually remove all the rows from a table and there will be no data in the table after we run the truncate command. 13. Can we use Truncate command on a table which is referenced by FOREIGN KEY? - No. We cannot use Truncate command on a table with Foreign Key because of referential integrity. 14. What is the use of DBCC commands? - DBCC stands for database consistency checker. We use these commands to check the consistency of the databases, i.e., maintenance, validation task and status checks. 15. Can you give me some DBCC command options?(Database consistency check) DBCC CHECKDB - Ensures that tables in the db and the indexes are correctly linked. and DBCC CHECKALLOC - To check that all pages in a db are correctly allocated. DBCC SQLPERF - It gives report on current usage of transaction log in
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percentage. DBCC CHECKFILEGROUP - Checks all tables file group for any damage. 16. What command do we use to rename a db? - sp_renamedb ‘oldname’ , ‘newname’ 17. Well sometimes sp_reanmedb may not work you know because if some one is using the db it will not accept this command so what do you think you can do in such cases? - In such cases we can first bring to db to single user using sp_dboptions and then we can rename that db and then we can rerun the sp_dboptions command to remove the single user mode. 18. What is the difference between a HAVING CLAUSE and a WHERE CLAUSE? Having Clause is basically used only with the GROUP BY function in a query. WHERE Clause is applied to each row before they are part of the GROUP BY function in a query. 19. What would you test when a new column is added in a table and there is a view already exists on that table? 20. What is a Join in SQL Server? - Join actually pu ts data from two or more tables into a single result set. 21. Can you explain the types of Joins that we can have with Sql Server? - There are three types of joins: Inner Join, Outer Join, Cross Join 22. When do you use SQL Profiler ? - SQL Profiler utility allows us to basically track connections to the SQL Server and also determine activities such as which SQL Scripts are running, failed jobs etc.. 23. What is a Linked Server ? - Linked Servers is a concept in SQL Server by which we can add other SQL Server to a Group and query both the SQL Server dbs using T-SQL Statements. 24. Write a query to display duplicate records? 25. Which stored procedure will you be running to add a linked server? sp_addlinkedserver , sp_addlinkedsrvlogin 26. What are the OS services that the SQL Server installation adds? - MS SQL SERVER SERVICE, SQL AGENT SERVICE, DTC (Distribution transac coordinator) 27. Can you explain the role of each service? - SQL SERVER - is for running the databases SQL AGENT - is for automation such as Jobs, DB Maintanance, Backups DTC - Is for linking and connecting to other SQL Servers 28. What are the authentication modes in SQL Server? - Windows mode and mixed mode (SQL & Windows). 29. Where do you think the user’s names and passwords will be stored in sql server? They get stored in master db in the sysxlogins table. 30. What is log shipping? Can we do logshipping with SQL Server 7.0 Logshipping is a new feature of SQL Server 2000. We should have two SQL Server - Enterprise Editions. From Enterprise Manager we can configure the logshipping. In logshipping the transactional log file from one server is automatically updated into the backup database on the other server. If one server fails, the other server will have the same db and we can use this as the DR (disaster recovery) plan. 31. Let us say the SQL Server crashed and you are rebuilding the databases including the master database what procedure to you follow? –
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For restoring the master db we have to stop the SQL Server first and then from command line we can type SQLSERVER –m which will basically bring it into the maintenance mode after which we can restore the master db. 32. Let us say master db itself has no backup. Now you have to rebuild the db so what kind of action do you take? - (I am not sure- but I think we have a command to do it). 33. What is BCP? When do we use it? - BulkCopy is a tool used to copy huge amount of data from tables and views. But it won’t copy the structures of the same. 34. What should we do to copy the tables, schema and views from one SQL Server to another? - We have to write some DTS packages for it. 35. What are the different types of joins and what d oes each do? 36. What are the four main query statements? 37. What is a sub-query? When would you use one? 38. What are three SQL keywords used to change or set someone’s permissions? 39. What is the difference between HAVING clause an d the WHERE clause? 40. What is referential integrity? What are the advantages of it? 41. What is database normalization? 42. Which command using Query Analyzer will give you the version of SQL server and operating system? 43. Using query analyzer, name 3 ways you can get an accurate count of the number of records in a table? 44. What is a trigger? 45. What is an execution plan? When would you use it? How would you view the execution plan? 46. What is the STUFF function and how does it differ from the REPLACE function? 47. What does it mean to have quoted_identifier on? What are the implications of having it off? 48. What are the different types of replication? How are they used? 49. What is the difference between a local and a global variable? 50. What is the difference between a Local temporary table and a Global temporary table? How is each one used? 51. What are cursors? Name four types of cursors and whe n each one would be applied? 52. What is the purpose of UPDATE STATISTICS? 53. How do you use DBCC statements to monitor various aspects of a SQL server installation? 54. How do you load large data to the SQL server database? 55. How do you check the performance of a query and how do you optimize it? 56. How do SQL server 2000 and XML linked? Can XML be used to access data? 57. What is SQL server agent? 58. What is referential integrity and how is it achieved? 59. What is indexing? 60. What is normalization and what are the different forms of normalizations? 61. Difference between server.transfer and server.execute method?
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62. What id de-normalization and when do you do it? 63. What is better - 2nd Normal form or 3rd normal form? Why? 64. Can we rewrite subqueries into simple select statements or with joins? Example? 65. What is a function? Give some example? 66. What is a stored procedure? 67. Difference between Function and Procedure-in general? 68. Difference between Function and Stored Procedure? 69. Can a stored procedure call another stored procedure. If yes what level and can it be controlled? 70. Can a stored procedure call itself(recursive). If yes what level and can it be controlled.? 71. How do you find the number of rows in a table? 72. Difference between Cluster and Non-cluster index? 73. What is a table called, if it does have neither Cluster nor Non-cluster Index? 74. Explain basic SQL queries with SELECT from where Order By, Group ByHaving? 75. Explain the basic concepts of SQL server architecture? 76. Explain couple pf features of SQL server 77. Scalability, Availability, Integration with internet, etc.)? 78. Explain fundamentals of Data ware housing & OLAP? 79. Explain the new features of SQL server 2000? 80. What is data integrity? Explain constraints? 81. Explain some DBCC commands? 82. Explain sp_configure commands, set commands? 83. Explain what are db_options used for? 84. What is the basic functions for master, msdb, tempdb databases? 85. What is a job? 86. What are tasks? 87. What are primary keys and foreign keys? 88. How would you Update the rows which are divisible by 10, given a set of numbers in column? 89. If a stored procedure is taking a table data type, how it looks? 90. How do you know which index a table is using? 91. How will you test the stored procedure taking two parameters namely first name and last name returning full name? 92. How do you find the error, how can you know the number of rows effected by last SQL statement? 93. How can you get @@error and @@rowcount at the same time? 94. What are sub-queries? Give example? In which case sub-queries are not feasible? 95. What are the types of joins? When do we use Outer and Self joins? 96. How do you measure the performance of a stored procedure? 97. Questions regarding Raiseerror? 98. Questions on identity? 99. If there is failure during updation of certain rows, what will be the state? 100. Various ways to count the number of records in a table and which is the fastest?
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101. Difference between truncate and delete and which is the fastest and what are the disadvantages of it? 102. Why do we go for recompile and when does recompile happen and how to force it? Various ways to force recompiling in the SP? 103. How will you find poorly performing queries? 104. How will tune the poorly performing queries? What are the strategies you follow? 105. Difference between subquery and Correlated subquery? 106. Different type of temporary tables 107. How Many indexes can be created in a view and what r the rules? 108. Architecture of your recent project? 109. how will you get XML output from sql queries 110. OLAP concepts? Star schema? 111. What is the process followed in the Development and unit testing? How do u document unit testing? 112. Have you worked on replication? What are the different types of replication? 113. How do I create a # table inside a trigger? 114. I want to create a # table without using create table #table name. How do I do that? 115. What are the drawbacks of using of using a # table? 116. I have Table A with two columns C1(primary key) & C2, I have used select * into Table B from Table B. Now I would like to compare the data is Table A and Table B. Please use the board and write a query? 117. Suppose I have Server A, and Server B. I want to read the data from Server B and insert data into a table in Server A. How would I do that? 118. What is the difference between the OLTP database and OLAP database? 119. Query to get employees hired between two given particular dates 120. x_Emp table: Emp_id Name Dept Supervisor
y_Emp table: Emp_id Payrate StartDate Enddate Write a query to get Emp name, supervisor, Payrate for all employees without using JOIN.
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Interview with Ken Agogila, Jagan, Renata and 2 more persons on 21st Nov at Samm-C 1. 2. 3. 4. 5. 6. 7.
Introduction, Previous project Roles and Responsibilities in the previous project Testing approach followed in the previous project What is the use of SET ROWCOUNT ? What is a Transaction? What is the difference between DELETE and TRUNCATE statements? There is a table called Emp and the data is sorted in the order of EmpID. Can we create a view on top of this table such that the data should be ordered on Salary? 8. What is a SubQuery and Corelated SubQuery? 9. There is a DELETE statement inside a transaction. What happens if the transaction is rolled back? 10. How do you test the schema of a table? Can you automate it? 11. What is metadata? 12. What is a cube? 13. What is a dimension table? 14. What is star schema? 15. What is snow-flake schema? 16. How do you validate the data? 17. There is a view and two users are accessing the same view. What will you do if one user asks for a schema change of the view? 18. What information is required to raise a bug? 19. If we ask you to learn Reporting services, what do you do. What is your approach? 20. There is a syntax error after executing a certain statement (which is new to you). What do you do? 21. Who is your MS manager for the previous project? 22. What is the bug that you found in the previous project that you can feel proud? There are many questions on the queries written by me. Eg: I wrote 2 separate SELECT statements. I was asked to write one SELECT statement by combining those 2 statements. I wrote a SELECT query with NOT IN clause. I was asked to write the same with Corelated subquery. ------------------------------------------------------------Interview with Ken Agogila, Renata on 18th Nov at Samm-C 1. Introduction, Previous project and description 2. Roles and responsibilities in the previous project 3. How do you test a DW application and how do you validate the data? 4. Write a query to get the highest empid from the Emp table which has million records? 5. Write a query to display the IDs which are there in table A but not in table B by using joins?
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6. Given a table Sales, write a query to display Type, count(Books) by category wise? 7. Write a query to eliminate null values? 8. Join tables Emp and Address, given some columns and asked to join using the primary key relation 9. Assume there is no single document for the project. How do you test that? 10. Given a deadline of one week and client asked a change in the table schema. What will you do? 11. Two users are accessing the same view. What will you do if one user wants a schema change of the view? 12. Database testing and UI testing, which you prefer more? 13. What is your achievement till now?
Interview with Jim Dutkiewicz and Manjunatha Shetty on 30 Nov at Building-109 1. Tell about yourself and previous experience 2. What are the types of joins 3. Write a query using self join 4. Write a query for managers table who has more than 5 records 5. How will you validate the data correctness between source and destination 6. What is the difference between OLTP and OLAP? 7. What is Cube,Fact,Dimension,measure? 8. How many facts can be created on a cube?why? 9. How will you test the reports? 10. What is the best bug you found in reports? 11. You don’t have any document, how will go about testing an application? 12. You have different machines with different operating systems and you are asked to install a software on all the machines but in some of the machines its not getting installed.how will you trobleshoot it? 13. If you click a submit button in a login form then you got a blank screen with out any error msg.How will you trobleshoot it? 14. Released 4 builds coming one after another and you have 1000 test cases.You had given option of executing 250 testcases for each build and all 1000 testcases for each build.which would you prefer and why? 15. You have 1 week of deadline but your test requires 3 weeks. what will you do? 16. Do you have any questions for us?
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MS SQL Server Interview Questions with Expected Answers
2.4.1.
Basics
What are the new features introduced in SQL Server 2000 (or the latest release of SQL Server at the time of your interview)? What changed between the previous version of SQL Server and the current version? This question is generally asked to see how current your knowledge is. Generally there is a section in the beginning of the books online titled "What's New", which has all such information. Of course, reading just that is not enou gh; you should have tried those things to better answer the questions. Also check out the section titled "Backward Compatibility" in books online which talks about the changes that have taken place in the new version. What are constraints? Explain different types of constraints. Constraints enable the RDBMS enforce the integrity of the d atabase automatically, without needing you to create triggers, rule or defaults. Types of constraints: NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY For an explanation of these constraints see books online for the pages titled: "Constraints" and "CREATE TABLE", "ALTER TABLE" What is an index? What are the types of indexes? How many clustered indexes can be created on a table? I create a separate index on each column of a table. what are the advantages and disadvantages of this approach? Indexes in SQL Server are similar to the indexes in books. They help SQL Server retrieve the data quicker. Indexes are of two types. Clustered indexes and non-clustered indexes. When you create a clustered index on a table, all the rows in the table are stored in the order of the clustered index key. So, there can be only one clustered index per table. Non-clustered indexes have their own storage separate from the table data storage. Non-clustered indexes are stored as B-tree structures (so do clustered indexe s), with the leaf level nodes having the index key and its row locater. The row located could be the RID or the Clustered index key, depending up on the absence or presence of clustered index on the table. If you create an index on each column of a table, it improves the query performance, as the query optimizer can choose from all the existing indexes to come up with an efficient execution plan. At the same time, data modification operations (such as INSERT, UPDATE, DELETE) will become slow, as every time data changes in the table, all the
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indexes need to be updated. Another disadvantage is that, indexes need disk space, the more indexes you have, more disk space is used. 2.4.2.
T-SQL Programming
Basic SELECT Statement
Write down the general syntax for a SELECT statement covering all the options. Here's the basic syntax: (Also checkout SELECT in books online for advanced syntax). SELECT select_list [INTO new_table_] FROM table_source [WHERE search_condition] [GROUP BY group_by_expression] [HAVING search_condition] [ORDER BY order_expression [ASC | DESC] ] JOINS
What is a join and explain different types of joins. Joins are used in queries to explain how different tables are related. Joins also let you select data from a table depending upon data from another table. Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER JOINS. For more information see pages from books on line titled: "Join Fundamentals" and "Using Joins". What is a self join? Explain it with an example. Self join is just like any other join, except that two instances of the same table will be joined in the query. Here is an example: Employees table which contains rows for n ormal employees as well as managers. So, to find out the managers of all the employees, you need a self join. CREATE TABLE emp ( empid int, mgrid int, empname char(10) ) INSERT emp SELECT 1,2,'Vyas' Confidential
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INSERT emp SELECT 2,3,'Mohan' INSERT emp SELECT 3,NULL,'Shobha' INSERT emp SELECT 4,2,'Shridhar' INSERT emp SELECT 5,2,'Sourabh' SELECT t1.empname [Employee], t2.empname [Manager] FROM emp t1, emp t2 WHERE t1.mgrid = t2.empid Here's an advanced query using a LEFT OUTER JOIN that even returns the employees without managers (super bosses) SELECT t1.empname [Employee], COALESCE(t2.empname, 'No manager') [Manager] FROM emp t1 LEFT OUTER JOIN emp t2 ON t1.mgrid = t2.empid Given an employee table, how would you find out the second highest salary? For a solution see the 'My code library' section of this site. How to join tables from different databases? You just have to qualify the table names in your SELECT queries with database name, followed by table owner name. In the following example, Table1 from pubs database and Table2 from northwind database are being joined on the column i. Both tables are owned by dbo. SELECT a.i, a.j FROM pubs.dbo.Table1 a INNER JOIN northwind.dbo.Table2 b ON a.i = b.i GO How to join tables from different servers? To be able to join tables between two SQL Servers, first you have to link them. After the linked servers are setup, you just have to prefix your tables names with server name, database name, table owner name in your SELECT queries. The following example links SERVER_01 to SERVER_02. Execute the following commands in SERVER_02: EXEC sp_addlinkedserver SERVER_01 GO
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/* The following command links 'sa' login on SERVER_02 with the 'sa' login of SERVER_01 */ EXEC sp_addlinkedsrvlogin @rmtsrvname = 'SERVER_01', @useself = 'false', @locallogin = 'sa', @rmtuser = 'sa', @rmtpassword = 'sa password of SERVER_01' GO SELECT a.title_id FROM SERVER_01.pubs.dbo.titles a INNER JOIN SERVER_02.pubs.dbo.titles b ON a.title_id = b.title_id GO Stored Procedures
How to get the complete error message from T-SQL while error handling? Unfortunately, the error handling capabilities of SQL Server are limited. When an error occurs, all you can get is the error number, using the @@ERROR global variable. There is no @@ERROR_MESSAGE global variable to get the error description. For a complete error message, you can always query the master..sysmessages table using the error number, but most of these messages have place holders (like %s, %l etc.), and hence we can't get the complete error message. However, the client applications using an object model such as RDO, ADO have access to the complete error message. How to get the first day of the week, last day of the week and last day of the month using T-SQL date functions? Here's the code: DECLARE @Date datetime SET @Date = '2001/08/31' SELECT DATEADD(dd,-(DATEPART(dw, @Date) - 1),@Date) AS 'First day of the week' SELECT DATEADD(dd,-(DATEPART(dw, @Date) - 7),@Date) AS 'Last day of the week' SELECT DAY(DATEADD(d, -DAY(DATEADD(m,1,@Date)),DATEADD(m,1,@Date))) AS 'Last day of the month' How to pass a table name, column name etc. to the stored procedure so that I can dynamically select from a table? Basically, SELECT and other commands like DROP TABLE won't let you use a variable instead of a hardcoded table name. To overcome this problem, you have to use dynamic
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sql. But dynamic SQL has some disadvantages. It's slow, as the dynamic SQL statement needs to be parsed everytime it's executed. Further, the user who is executing the dynamic SQL string needs direct permissions on the tables, which defeats the purpose of having stored procedures to mask the underlying tables. Having said that, here are some examples of dynamic SQL: (Also see sp_executesql in SQL Server Books Online) CREATE PROC DropTable @Table sysname AS EXEC ('DROP TABLE ' + @Table) GO EXEC DropTable 'MyTable' GO CREATE PROC SelectTable @Table sysname AS EXEC ('SELECT * FROM ' + @Table) GO EXEC SelectTable 'MyTable' For a complete discussion on the pros and cons of dynamic SQL check out Erland's article: The curse and blessings of dynamic SQL How to save the output of a query/stored procedure to a text file using T-SQL? T-SQL by itself has no support for saving the ou tput of queries/stored procedures to text files. But you could achieve this using the command line utilities like isql.exe and osql.exe. You could either invoke these exe files directly from command prompt/batch files or from T-SQL using the xp_cmdshell command. Here are the examples: From command prompt: osql.exe -S YourServerName -U sa -P secretcode -Q "EXEC sp_who2" -o "E:\output.txt" From T-SQL: EXEC master..xp_cmdshell 'osql.exe -S YourServerName -U sa -P secretcode -Q "EXEC sp_who2" -o "E:\output.txt"' Query Analyzer lets you save the query output to text files manually. The output of stored procedures that are run as a part of a scheduled job, can also be saved to a text file. BCP and Data Transformation Services (DTS) let you export table data to text files.
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What are cursors? Explain different types of cursors. What are the disadvantages of cursors? How can you avoid cursors? Cursors allow row-by-row processing of the resultsets. Types of cursors: Static, Dynamic, Forward-only, Keyset-driven. See books online for more information. Disadvantages of cursors: Each time you fetch a row from the cursor, it results in a network roundtrip, where as a normal SELECT query makes only one rowundtrip, however large the resultset is. Cursors are also costly because they require more resources and temporary storage (results in more IO operations). Furthere, there are restrictions on the SELECT statements that can be used with some types of cursors. Most of the times, set based operations can be used instead of cursors. Here is an example: If you have to give a flat hike to your employees using the following criteria: Salary between 30000 and 40000 -- 5000 hike Salary between 40000 and 55000 -- 7000 hike Salary between 55000 and 65000 -- 9000 hike In this situation many developers tend to use a cursor, determine each employee's salary and update his salary according to the above formula. But the same can be achieved by multiple update statements or can be combined in a single UPDATE statement as shown below: UPDATE tbl_emp SET salary = CASE WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000 WHEN salary BETWEEN 40000 AND 55000 THEN salary + 7000 WHEN salary BETWEEN 55000 AND 65000 THEN salary + 10000 END Another situation in which developers tend to use cursors: You need to call a stored procedure when a column in a particular row meets certain condition. You don't have to use cursors for this. This can be achieved using WHILE loop, as long as there is a unique key to identify each row. For examples of using WHILE loop for row by row processing, check out the 'My code library' section of my site or search for WHILE. Triggers
What are triggers? How many triggers you can hav e on a table? How to invoke a trigger on demand? Triggers are special kind of stored procedures that get executed automatically when an INSERT, UPDATE or DELETE operation takes place on a table.
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In SQL Server 6.5 you could define only 3 triggers per table, one for INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this restriction is gone, and you could create multiple triggers per each action. But in 7.0 there's no way to control the order in which the triggers fire. In SQL Server 2000 you could specify which trigger fires first or fires last using sp_settriggerorder Triggers can't be invoked on demand. They get triggered only when an associated action (INSERT, UPDATE, DELETE) happens on the table on which they are defined. Triggers are generally used to implement business rules, auditing. Triggers can also be used to extend the referential integrity checks, but wherever possible, use constraints for this purpose, instead of triggers, as constraints are much faster. Till SQL Server 7.0, triggers fire only after the data modification operation happens. So in a way, they are called post triggers. But in SQL Server 2000 you could create pre triggers also. Search SQL Server 2000 books online for INSTEAD OF triggers. Also check out books online for 'inserted table', 'deleted table' and COLUMNS_UPDATED() How to programmatically find out when the SQL Server service started? Everytime SQL Server starts, it recreates the tempdb database. So, the creation date and time of the tempdb database tells us the date and time at which SQL Server service started. This information is stored in the crdate column of the sysdatabases table in master database. Here's the query to find that out: SELECT crdate AS 'SQL Server service started approximately at:' FROM master.dbo.sysdatabases WHERE name = 'tempdb' SQL Server error log also has this information (This is more accurate) and the error log can be queried using xp_readerrorlog How to get rid of the time part from the date returned by GETDATE function? We have to use the CONVERT function to strip the time off the d ate. Any of the following commands will do this: SELECT CONVERT(char,GETDATE(),101) SELECT CONVERT(char,GETDATE(),102) SELECT CONVERT(char,GETDATE(),103) SELECT CONVERT(char,GETDATE(),1) See SQL Server Books Online for more information on CONVERT function.
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How to run an SQL script file that is located on the disk, using T-SQL? There's no direct command to read a script file and execute it. But the isql.exe and osql.exe come in handy when you have to execute a script file from within T-SQL. Just call any of these exes using xp_cmdshell and pass the script file name as parameter to it. See SQL Server Books Online for more information about the input parameters of these exes. Here are some quick examples: EXEC master..xp_cmdshell 'osql -Svaio -Usa -Pzaassds1 -ic:\MySQl.sql -n' EXEC master..xp_cmdshell 'isql -Svaio -Usa -Pzaassds1 -ic:\MySQl.sql -n' See xp_cmdshell in SQL Server Books Online if you are having permissions problems in getting this technique to work. Miscellaneous
Why are my insert, update statements failing with the following error? Server: Msg 8152, Level 16, State 9, Line 1 String or binary data would be truncated. The statement has been terminated. This error occurs, when the length of the value entered by you into a char, varchar, nchar, nvarchar column is longer than the maximum length of the column. For example, inserting 'FAQ' into a char(2) column would result in this error. Profiler is handy in troubleshooting this error. If data truncation is okay with you an d you don't want to see this error, then turn off ANSI WARNINGS by using the following SET command: SET ANSI_WARNINGS OFF. Steps to reproduce the problem: CREATE TABLE MyTable ( Pkey int PRIMARY KEY, Col1 char(10) ) GO INSERT INTO MyTable (Pkey, Col1) VALUES (1, 'SQL Server Clustering FAQ') GO Make sure, you restrict the length of input, in your front-end applications. For example, you could use the MAXLENGTH property of the text boxes in HTML forms. E.g: How to convert timestamp data to date data (datetime datatype)?
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The name timestamp is a little misleading. Timestamp data has nothing to do with dates and times and can not be converted to date data. A timestamp is a unique number within the database and is equivalent to a binary(8)/varbinary(8) datatype. A table can have only one timestamp column. Timestamp value of a row changes with every update of the row. To avoid the confusion, SQL Server 2000 introduced a synonym to timestamp, called rowversion. How to run jobs from T-SQL? Use the procedure msdb..sp_start_job to start jobs programmatically. See SQL Server Books Online for more information. I forgot/lost the sa password. What to do? Forgot or lost your sa password? Don't worry, there is a way o ut :) Login to the SQL Server computer as the Administrator of that computer. Open Query Analyzer and connect to SQL Server using Windows NT authentication. Run sp_password as show below to reset the sa password: sp_password @new = 'will_never_forget_again', @loginame = 'sa' Can you have a nested transaction? Yes, very much. Check out BEGIN TRAN, COMMIT, ROLLBACK, SAVE TRAN and @@TRANCOUNT What is the system function to get the current user's user id? USER_ID(). Also check out other system functions like USER_NAME(), SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID(), HOST_NAME().
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3. SQL Server 2000 Reading Material This reading material is intended to provide basic knowledge in SQL Server 2000 for the testers. * For core SQL Server topics, go through MS_SQL_Server_Preparation_Guide.doc. * Sometimes client may require testers who have knowledge in the Data warehousing. Having basic conceptual knowledge is sufficient to face the interview. Refer OLAP_Interview_Questions.doc The above documents can be acquired from TCS resource manager. 3.1.
Database Normalization Basics
If you've been working with databases for a while, chances are you've heard the term normalization. Perhaps someone's asked you "Is that database normalized?" or "Is that in BCNF?" All too often, the reply is "Uh, yeah." Normalization is often brushed aside as a luxury that only academics have time for. However, knowing the principles of normalization and applying them to your daily database design tasks really isn't all that complicated and it could drastically improve the performance of your DBMS. In this article, we'll introduce the concept of normalization and take a brief look at the most common normal forms. Future articles will provide in-depth explorations of the normalization process. So, what is normalization? Basically, it's the process of efficiently organizing data in a database. There are two goals of the normalization process: eliminate redundant data (for example, storing the same data in more than one table) and ensure data dependencies make sense (only storing related data in a table). Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored. The database community has developed a series of guidelines for ensuring that databases are normalized. These are referred to as normal forms and are numbered from one (the lowest form of normalization, referred to as first normal form or 1NF) through five (fifth normal form or 5NF). In practical applications, you'll often see 1NF, 2NF, and 3NF along with the occasional 4NF. Fifth normal form is very rarely seen and won't be discussed in this article. Before we begin our discussion of the normal forms, it's important to point out that they are guidelines and guidelines only. Occasionally, it becomes necessary to stray from them to meet practical business requirements. However, when variations take place, it's extremely important to evaluate any possible ramifications they could have on your system and account for possible inconsistencies. That said, let's explore the normal forms.
First normal form (1NF) sets the very basic rules for an organized database:
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Eliminate duplicative columns from the same table. Create separate tables for each group of related data and identify each row with a unique column or set of columns (the primary key).
Second normal form (2NF) further addresses the concept of removing duplicative data: •
•
Remove subsets of data that apply to multiple rows of a table and place them in separate tables. Create relationships between these new tables and their predecessors through the use of foreign keys.
Third normal form (3NF) goes one large step further: •
Remove columns that are not dependent upon the primary key.
Finally, fourth normal form (4NF) has one requirement: •
A relation is in 4NF if it has no multi-valued dependencies.
Remember, these normalization guidelines are cumulative. For a database to be in 2NF, it must first fulfill all the criteria of a 1NF database.
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Physical Database Organization
3.2.1.
Table and Index Architecture
Objects in a Microsoft® SQL Server™ 2000 database are stored as a collection of 8-KB pages. This topic describes the way the pages for tables and indexes are organized. SQL Server 2000 supports indexes on views. The first index allowed on a view is a clustered index. At the time a CREATE INDEX statement is executed on a view, the result set for the view is materialized and stored in the database with the same structure as a table that has a clustered index. The result set that is stored is the same as that which is produced by this statement. SELECT * FROM ViewName The data rows for each table or indexed view are stored in a collection of 8-KB data pages. Each data page has a 96-byte header containing system information such as the identifier (ID) of the table that owns the page. The page header also includes pointers to the next and previous pages that are used if the pages are linked in a list. A row offset table is at the end of the page. Data rows fill the rest of the page. 3.2.2.
Organization of Data Pages
SQL Server 2000 tables use one of two methods to organize their data pages: •
Clustered tables are tables that have a clustered index. The data rows are stored in order based on the clustered index key. The index is implemented as a B-tree index structure that supports fast retrieval of the rows based on their clustered index key values. The pages in each level of the index, including the data pages in the leaf level, are linked in a doubly-linked list, but navigation from one level to another is done using key values.
•
Heaps are tables that have no clustered index. The data rows are not stored in any particular order, and there is no particular order to the sequence of the data pages. The data pages are not linked in a linked list.
Indexed views have the same storage structure as clustered tables. SQL Server also supports up to 249 nonclustered indexes on each table or indexed view. The nonclustered indexes have a B-tree index structure similar to the one in clustered indexes. The difference is that nonclustered indexes have no effect on the order of the data rows. Clustered tables and indexed views keep their data rows in order based on the
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clustered index key. The collection of data pages for a heap is not affected if nonclustered indexes are defined for the table. The data pages remain in a heap unless a clustered index is defined. The pages holding text, ntext, and image data are managed as a single unit for each table. All of the text, ntext, and image data for a table is stored in one collection of pages. All of the page collections for tables, indexes and indexed views are anchored by page pointers in the sysindexes table. Every table and indexed view has one collection of data pages, plus additional collections of pages to implement each index defined for the table or view. Each table, index and indexed view has a row in sysindexes uniquely identified by the combination of the object identifier (id) column and the index identifier (indid) column. The allocation of pages to tables, indexes, and indexed views is managed by a chain of IAM pages. The column sysindexes.FirstIAM points to first IAM page in the chain of IAM pages managing the space allocated to the table, index or indexed view. Each table has a set of rows in sysindexes : •
A heap has a row in sysindexes with indid = 0. The FirstIAM column points to the IAM chain for the collection of data pages for the table. The server uses the IAM pages to find the pages in the data page collection because they are not linked together.
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A clustered index on a table or view has a row in sysindexes with indid = 1. The root column points to the top of the clustered index B-tree. The server uses the index B-tree to find the data pages.
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Each nonclustered index created for a table or view has a row in sysindexes . The values for indid in the rows for each nonclustered index range from 2 through 250. The root column points to the top of the nonclustered index B-tree.
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Each table that has at least one text, ntext, or image column also has a row in sysindexes with indid = 255. The column FirstIAM points to the chain of IAM pages that manage the text, ntext, and image pages.
In SQL Server version 6.5 and earlier, sysindexes.first always points to the start of a heap, the start of the leaf level of an index, or the start of a chain of text and image pages. In SQL Server version 7.0 and later, sysindexes.first is largely unused. In SQL
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Server version 6.5 and earlier, sysindexes.root in a row with indid = 0 points to the last page in a heap. In SQL Server version 7.0 and later, sysindexes.root in a row with indid = 0 is unused. 3.3.
Indexes
Indexes in databases are similar to indexes in books. In a book, an index allows you to find information quickly without reading the entire book. In a database, an index allows the database program to find data in a table without scanning the entire table. An index in a book is a list of words with the page numbers that contain each word. An index in a database is a list of values in a table with the storage locations of rows in the table that contain each value. Indexes can be created on either a single column or a combination of columns in a table and are implemented in the form of B-trees. An index contains an entry with one or more columns (the search key) from each row in a table. A B-tree is sorted on the search key, and can be searched efficiently on any leading subset of the search key. For example, an index on columns A, B, C can be searched efficiently on A, on A, B, and A, B, C. Most books contain one general index of words, names, places, and so on. Databases contain individual indexes for selected types or columns of data: this is similar to a book that contains one index for names of people and another index for places. When you create a database and tune it for performance, you should create indexes for the columns used in queries to find data. In the pubs sample database provided with Microsoft® SQL Server™ 2000, the employee table has an index on the emp_id column. The following illustration shows how the index stores each emp_id value and points to the rows of data in the table with each value. When SQL Server executes a statement to find data in the employee table based on a specified emp_id value, it recognizes the index for the emp_id column and uses the index to find the data. If the index is not present, it performs a full table scan starting at the beginning of the table and stepping through each row, searching for the specified emp_id value. SQL Server automatically creates indexes for certain types of constraints (for example, PRIMARY KEY and UNIQUE constraints). You can further customize the table definitions by creating indexes that are independent of constraints. The performance benefits of indexes, however, do come with a cost. Tables with indexes require more storage space in the database. Also, commands that insert, update, or delete data can take longer and require more processing time to maintain the indexes. When you design and create indexes, you should ensure that the performance benefits outweigh the extra cost in storage space and processing resources.
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Clustered Indexes
Clustered indexes have one row in sysindexes with indid = 1. The pages in the data chain and the rows in them are ordered on the value of the clustered index key. All inserts are made at the point the key value in the inserted row fits in the ordering sequence. Microsoft® SQL Server™ 2000 indexes are organized as B-trees. Each page in an index holds a page header followed by index rows. Each index row contains a key value and a pointer to either a lower-level page or a data row. Each page in an index is called an index node. The top node of the B-tree is called the root node. The bottom layer of nodes in the index are called the leaf nodes. The pages in each level of the index are linked together in a doubly-linked list. In a clustered index, the data pages make up the leaf nodes. Any index levels between the root and the leaves are collectively known as intermediate levels. For a clustered index, sysindexes.root points to the top of the clustered index. SQL Server navigates down the index to find the row corresponding to a clustered index key. To find a range of keys, SQL Server navigates through the index to find the starting key value in the range, and then scans through the data pages using the previous or next pointers. To find the first page in the chain of data pages, SQL Server follows the leftmost pointers from the root node of the index. This illustration shows the structure of a clustered index. 3.3.2.
Nonclustered Indexes
Nonclustered indexes have the same B-tree structure as clustered indexes, with two significant differences: •
The data rows are not sorted and stored in order based on their nonclustered keys.
•
The leaf layer of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows. Each index row contains the nonclustered key value and one or more row locators that point to the data row (or rows if the index is not unique) having the key value.
Nonclustered indexes can be defined on a table with a clustered index, a heap, or an indexed view. In Microsoft® SQL Server™ 2000, the row locators in nonclustered index rows have two forms: •
•
If the table is a heap (does not have a clustered index), the row locator is a pointer to the row. The pointer is built from the file identifier (ID), page number, and number of the row on the page. The entire pointer is known as a Row ID. If the table does have a clustered index, or the index is on an indexed view, the row locator is the clustered index key for the row. If the clustered index is not a Confidential
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unique index, SQL Server 2000 makes duplicate keys unique by adding an internally generated value. This value is not visible to users; it is used to make the key unique for use in nonclustered indexes. SQL Server retrieves the data row by searching the clustered index using the clustered index key stored in the leaf row of the nonclustered index. Because nonclustered indexes store clustered index keys as their row locators, it is important to keep clustered index keys as small as possible. Do not choose large columns as the keys to clustered indexes if a table also has nonclustered indexes. 3.4.
Using Joins
Join conditions can be specified in either the FROM or WHERE clauses; specifying them in the FROM clause is recommended. WHERE and HAVING clauses can also contain search conditions to further filter the rows selected by the join conditions. Joins can be categorized as: •
Inner joins (the typical join operation, which uses some comparison operator like = or <>). These include equi-joins and natural joins. Inner joins use a comparison operator to match rows from two tables based on the values in common columns from each table. For example, retrieving all rows where the student identification number is the same in both the students and courses tables.
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Outer joins. Outer joins can be a left, a right, or full outer join. Outer joins are specified with one of the following sets of keywords when they are specified in the FROM clause: •
LEFT JOIN or LEFT OUTER JOIN The result set of a left outer join includes all the rows from the left table specified in the LEFT OUTER clause, not just the ones in which the joined columns match. When a row in the left table has no matching rows in the right table, the associated result set row contains null values for all select list columns coming from the right table.
•
RIGHT JOIN or RIGHT OUTER JOIN. A right outer join is the reverse of a left outer join. All rows from the right table are returned. Null values are returned for the left table any time a right table row has no matching row in the left table.
•
FULL JOIN or FULL OUTER JOIN.
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A full outer join returns all rows in both the left and right tables. Any time a row has no match in the other table, the select list columns from the other table contain null values. When there is a match between the tables, the entire result set row contains data values from the base tables. •
Cross joins. Cross joins return all rows from the left table, each row from the left table is combined with all rows from the right table. Cross joins are also called Cartesian products.
For example, here is an inner join retrieving the authors who live in the same city and state as a publisher: USE pubs SELECT a.au_fname, a.au_lname, p.pub_name FROM authors AS a INNER JOIN publishers AS p ON a.city = p.city AND a.state = p.state ORDER BY a.au_lname ASC, a.au_fname ASC The tables or views in the FROM clause can be specified in any order with an inner join or full outer join; however, the order of tables or views specified when using either a left or right outer join is important. For more information about table ordering with left or right outer joins, see Using Outer Joins. 3.4.1.
Using Cross Joins
A cross join that does not have a WHERE clause produces the Cartesian product of the tables involved in the join. The size of a Cartesian product result set is the number of rows in the first table multiplied by the number of rows in the second table. This is an example of a Transact-SQL cross join: USE pubs SELECT au_fname, au_lname, pub_name FROM authors CROSS JOIN publishers ORDER BY au_lname DESC The result set contains 184 rows (authors has 23 rows and publishers has 8; 23 multiplied by 8 equals 184). However, if a WHERE clause is added, the cross join behaves as an inner join. For example, these Transact-SQL queries produce the same result set: USE pubs SELECT au_fname, au_lname, pub_name
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FROM authors CROSS JOIN publishers WHERE authors.city = publishers.city ORDER BY au_lname DESC -- Or USE pubs SELECT au_fname, au_lname, pub_name FROM authors INNER JOIN publishers ON authors.city = publishers.city ORDER BY au_lname DESC 3.4.2.
Null Values and Joins
When there are null values in the columns of the tables being joined, the null values do not match each other. The presence of null values in a column from one of the tables being joined can be returned only by using an outer join (unless the WHERE clause excludes null values). Here are two tables that each have NULL in the column that will participate in the join: table1 a b ------- -----1 one NULL three 4 join4
table2 c
d -----------NULL two 4 four
A join that compares the values in column a against column c does not get a match on the columns that have values of NULL: SELECT * FROM table1 t1 JOIN table2 t2 ON t1.a = t2.c ORDER BY t1.a Only one row with 4 in column a and c is returned: a b c d ----------- ------ ----------- -----4 join4 4 four (1 row(s) affected) Null values returned from a base table are also difficult to distinguish from the null values returned from an outer join. For example, this SELECT statement does a left outer join on these two tables:
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SELECT * FROM table1 t1 LEFT OUTER JOIN table2 t2 ON t1.a = t2.c ORDER BY t1.a Here is the result set: a b c d ----------- ------ ----------- ----- NULL three NULL NULL 1 one NULL NULL 4 join4 4 four (3 row(s) affected) The results do not make it easy to distinguish a NULL in the data from a NULL that represents a failure to join. When null values are present in data being joined, it is usually preferable to omit them from the results by using a regular join. 3.4.3.
Using Outer Joins
Inner joins return rows only when there is at least one row from both tables that matches the join condition. Inner joins eliminate the rows that do not match with a row from the other table. Outer joins, however, return all rows from at least one of the tables or views mentioned in the FROM clause, as long as those rows meet any WHERE or HAVING search conditions. All rows are retrieved from the left table referenced with a left outer join, and all rows from the right table referenced in a right outer join. All rows from both tables are returned in a full outer join Microsoft® SQL Server™ 2000 uses these SQL-92 keywords for outer joins specified in a FROM clause: •
LEFT OUTER JOIN or LEFT JOIN
•
RIGHT OUTER JOIN or RIGHT JOIN
•
FULL OUTER JOIN or FULL JOIN
SQL Server supports both the SQL-92 outer join syntax and a legacy syntax for specifying outer joins based on using the *= and =* operators in the WHERE clause. The SQL-92 syntax is recommended because it is not subject to the ambiguity that sometimes results from the legacy Transact-SQL outer joins. 3.4.4.
Using Left Outer Joins
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Consider a join of the authors table and the publishers table on their city columns. The results show only the authors who live in cities in which a publisher is located (in this case, Abraham Bennet and Cheryl Carson). To include all authors in the results, regardless of whether a publisher is located in the same city, use an SQL-92 left outer join. The following is the query and results of the Transact-SQL left outer join: USE pubs SELECT a.au_fname, a.au_lname, p.pub_name FROM authors a LEFT OUTER JOIN publishers p ON a.city = p.city ORDER BY p.pub_name ASC, a.au_lname ASC, a.au_fname ASC Here is the result set: au_fname au_lname pub_name -------------------- ------------------------------ ----------------Reginald Blotchet-Halls NULL Michel DeFrance NULL Innes del Castillo NULL Ann Dull NULL Marjorie Green NULL Morningstar Greene NULL Burt Gringlesby NULL Sheryl Hunter NULL Livia Karsen NULL Charlene Locksley NULL Stearns MacFeather NULL Heather McBadden NULL Michael O'Leary NULL Sylvia Panteley NULL Albert Ringer NULL Anne Ringer NULL Meander Smith NULL Dean Straight NULL Dirk Stringer NULL Johnson White NULL Akiko Yokomoto NULL Abraham Bennet Algodata Infosystems Cheryl Carson Algodata Infosystems (23 row(s) affected) The LEFT OUTER JOIN includes all rows in the authors table in the results, whether or not there is a match on the city column in the publishers table. Notice that in the results
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there is no matching data for most of the authors listed; therefore, these rows contain null values in the pub_name column. 3.4.5.
Using Right Outer Joins
Consider a join of the authors table and the publishers table on their city columns. The results show only the authors who live in cities where a publisher is located (in this case, Abraham Bennet and Cheryl Carson). The SQL-92 right outer join operator, RIGHT OUTER JOIN, indicates all rows in the second table are to be included in the results, regardless of whether there is matching data in the first table. To include all publishers in the results, regardless of whether a city has a publisher located in the same city, use an SQL-92 right outer join. Here is the Transact-SQL query and results of the right outer join: USE pubs SELECT a.au_fname, a.au_lname, p.pub_name FROM authors AS a RIGHT OUTER JOIN publishers AS p ON a.city = p.city ORDER BY p.pub_name ASC, a.au_lname ASC, a.au_fname ASC Here is the result set: au_fname au_lname pub_name -------------------- ------------------------ -------------------Abraham Bennet Algodata Infosystems Cheryl Carson Algodata Infosystems NULL NULL Binnet & Hardley NULL NULL Five Lakes Publishing NULL NULL GGG&G NULL NULL Lucerne Publishing NULL NULL New Moon Books NULL NULL Ramona Publishers NULL NULL Scootney Books (9 row(s) affected) An outer join can be further restricted by using a predicate (such as comparing the join to a constant). This example contains the same right outer join, but eliminates all titles that have sold fewer than 50 copies: USE pubs SELECT s.stor_id, s.qty, t.title FROM sales s RIGHT OUTER JOIN titles t ON s.title_id = t.title_id AND s.qty > 50 ORDER BY s.stor_id ASC Confidential
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Here is the result set: stor_id qty title ------- ------ --------------------------------------------------------(null) (null) But Is It User Friendly? (null) (null) Computer Phobic AND Non-Phobic Individuals: Behavior Variations (null) (null) Cooking with Computers: Surreptitious Balance Sheets (null) (null) Emotional Security: A New Algorithm (null) (null) Fifty Years in Buckingham Palace Kitchens 7066 75 Is Anger the Enemy? (null) (null) Life Without Fear (null) (null) Net Etiquette (null) (null) Onions, Leeks, and Garlic: Cooking Secrets of the Mediterranean (null) (null) Prolonged Data Deprivation: Four Case Studies (null) (null) Secrets of Silicon Valley (null) (null) Silicon Valley Gastronomic Treats (null) (null) Straight Talk About Computers (null) (null) Sushi, Anyone? (null) (null) The Busy Executive's Database Guide (null) (null) The Gourmet Microwave (null) (null) The Psychology of Computer Cooking (null) (null) You Can Combat Computer Stress! (18 row(s) affected) For more information about predicates, see WHERE. 3.4.6.
Using Full Outer Joins
To retain the nonmatching information by including nonmatching rows in the results of a join, use a full outer join. Microsoft® SQL Server™ 2000 provides the full outer join operator, FULL OUTER JOIN, which includes all rows from both tables, regardless of whether or not the other table has a matching value. Consider a join of the authors table and the publishers table on their city columns. The results show only the authors who live in cities in which a publisher is located (in this case, Abraham Bennet and Cheryl Carson). The SQL-92 FULL OUTER JOIN operator indicates that all rows from both tables are to be included in the results, regardless of whether there is matching data in the tables. To include all publishers and all authors in the results, regardless of whether a city has a publisher located in the same city, or whether a publisher is located in the same city, use a full outer join. The following is the query and results of the Transact-SQL full outer join:
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USE pubs SELECT a.au_fname, a.au_lname, p.pub_name FROM authors a FULL OUTER JOIN publishers p ON a.city = p.city ORDER BY p.pub_name ASC, a.au_lname ASC, a.au_fname ASC Here is the result set: au_fname au_lname pub_name -------------------- ---------------------------- -------------------Reginald Blotchet-Halls NULL Michel DeFrance NULL Innes del Castillo NULL Ann Dull NULL Marjorie Green NULL Morningstar Greene NULL Burt Gringlesby NULL Sheryl Hunter NULL Livia Karsen NULL Charlene Locksley NULL Stearns MacFeather NULL Heather McBadden NULL Michael O'Leary NULL Sylvia Panteley NULL Albert Ringer NULL Anne Ringer NULL Meander Smith NULL Dean Straight NULL Dirk Stringer NULL Johnson White NULL Akiko Yokomoto NULL Abraham Bennet Algodata Infosystems Cheryl Carson Algodata Infosystems NULL NULL Binnet & Hardley NULL NULL Five Lakes Publishing NULL NULL GGG&G NULL NULL Lucerne Publishing NULL NULL New Moon Books NULL NULL Ramona Publishers NULL NULL Scootney Books (30 row(s) affected) 3.4.7.
Using Self-Joins
A table can be joined to itself in a self-join. For example, you can use a self-join to find out the authors in Oakland, California who live in the same ZIP Code area. Confidential
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Because this query involves a join of the authors table with itself, the authors table appears in two roles. To distinguish these roles, you must give the authors table two different aliases (au1 and au2) in the FROM clause. These aliases are used to qualify the column names in the rest of the query. This is an example of the self-join Transact-SQL statement: USE pubs SELECT au1.au_fname, au1.au_lname, au2.au_fname, au2.au_lname FROM authors au1 INNER JOIN authors au2 ON au1.zip = au2.zip WHERE au1.city = 'Oakland' ORDER BY au1.au_fname ASC, au1.au_lname ASC Here is the result set: au_fname au_lname au_fname au_lname -------------------- ------------------- -------------------- --------Dean Straight Dean Straight Dean Straight Dirk Stringer Dean Straight Livia Karsen Dirk Stringer Dean Straight Dirk Stringer Dirk Stringer Dirk Stringer Livia Karsen Livia Karsen Dean Straight Livia Karsen Dirk Stringer Livia Karsen Livia Karsen Marjorie Green Marjorie Green Stearns MacFeather Stearns MacFeather (11 row(s) affected) To eliminate the rows in the results in which the authors match themselves and to eliminate rows that are identical, except the order of the authors is reversed, make this change to the Transact-SQL self-join query: USE pubs SELECT au1.au_fname, au1.au_lname, au2.au_fname, au2.au_lname FROM authors au1 INNER JOIN authors au2 ON au1.zip = au2.zip WHERE au1.city = 'Oakland' AND au1.state = 'CA' AND au1.au_id < au2.au_id ORDER BY au1.au_lname ASC, au1.au_fname ASC Here is the result set: au_fname
au_lname
au_fname
au_lname
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------------ ----------------- -------------------- -------------------Dean Straight Dirk Stringer Dean Straight Livia Karsen Dirk Stringer Livia Karsen (3 row(s) affected) It is now clear that Dean Straight, Dirk Stringer, and Livia Karsen all have the same ZIP Code and live in Oakland, California. 3.5.
Constraints
Constraints allow you to define the way Microsoft® SQL Server™ 2000 automatically enforces the integrity of a database. Constraints define rules regarding the values allowed in columns and are the standard mechanism for enforcing integrity. Using constraints is preferred to using triggers, rules, and defaults. The query optimizer also uses constraint definitions to build high-performance query execution plans. 3.5.1.
Classes of Constraints
SQL Server 2000 supports five classes of constraints. •
•
NOT NULL specifies that the column does not accept NULL values. CHECK constraints enforce domain integrity by limiting the values that can be placed in a column. A CHECK constraint specifies a Boolean (evaluates to TRUE or FALSE) search condition that is applied to all values entered for the column; all values that do not evaluate to TRUE are rejected. You can specify multiple CHECK constraints for each column. This sample shows the creation of a named constraint, chk_id, that further enforces the domain of the primary key by ensuring that only numbers within a specified range are entered for the key. CREATE TABLE cust_sample ( cust_id int PRIMARY KEY, cust_name char(50), cust_address char(50), cust_credit_limit money, CONSTRAINT chk_id CHECK (cust_id BETWEEN 0 and 10000 ) )
•
UNIQUE constraints enforce the uniqueness of the values in a set of columns. No two rows in the table are allowed to have the same not null values for the columns in a UNIQUE constraint. Primary keys also enforce uniqueness, but
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primary keys do not allow null values. A UNIQUE co nstraint is preferred over a unique index. •
PRIMARY KEY constraints identify the column or set of columns whose values uniquely identify a row in a table. No two rows in a table can have the same primary key value. You cannot enter a NULL for any column in a primary key. NULL is a special value in databases that represents an unknown value, which is distinct from a blank or 0 value. Using a small, integer column as a primary key is recommended. Each table should have a primary key. A table may have more than one combination of columns that could uniquely identify the rows in a table; each combination is a candidate key. The database administrator picks one of the candidate keys to be the primary key. For example, in the part_sample table both part_nmbr and part_name could be candidate keys, but only part_nmbr is chosen as a primary key. CREATE TABLE part_sample (part_nmbr int PRIMARY KEY, part_name char(30), part_weight decimal(6,2), part_color char(15) )
•
FOREIGN KEY constraints identify the relationships between tables. A foreign key in one table points to a candidate key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no candidate keys with that value. In the following sample, the order_part table establishes a foreign key referencing the part_sample table defined earlier. Usually, order_part would also have a foreign key against an order table, but this is a simple example. CREATE TABLE order_part (order_nmbr int, part_nmbr int FOREIGN KEY REFERENCES part_sample(part_nmbr) ON DELETE NO ACTION, qty_ordered int) GO You cannot insert a row with a foreign key value (except NULL) if there is n o candidate key with that value. The ON DELETE clause controls what actions are taken if you attempt to delete a row to which existing foreign keys point. The ON DELETE clause has two options:
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NO ACTION specifies that the deletion fails with an error. CASCADE specifies that all the rows with foreign keys pointing to the deleted row are also deleted.
The ON UPDATE clause defines the actions that are taken if you attempt to update a candidate key value to which existing foreign keys point. It also supports the NO ACTION and CASCADE options. 3.5.2.
Column and Table Constraints
Constraints can be column constraints or table constraints: •
•
A column constraint is specified as part of a column definition and applies only to that column (the constraints in the earlier samples are column constraints). A table constraint is declared independently from a column definition and can apply to more than one column in a table.
Table constraints must be used when more than one column must be included in a constraint. For example, if a table has two or more columns in the primary key, you must use a table constraint to include both columns in the primary key. Consider a table that records events happening in a computer in a factory. Assume that events of several types can happen at the same time, but that no two events happening at the same time can be of the same type. This can be enforced in the table by including both the type and time columns in a two-column primary key. CREATE TABLE factory_process (event_type int, event_time datetime, event_site char(50), event_desc char(1024), CONSTRAINT event_key PRIMARY KEY (event_type, event_time) )
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SQL Server security model
Security is a major concern for the modern age systems/network/database administrators. It is natural for an administrator to worry about hackers and external attacks while implementing security. But there is more to it. It is essential to first implement security within the organization, to make sure right people have access to the right data. Without these security measures in place, you might find someone destroying your valuable data, or selling your company's secrets to your competitors or someone invading the privacy of others. Primarily a security plan must identify which users in the organization can see which data and perform which activities in the database. To be able to access data from a database, a user must pass through two stages of authentication, one at the SQL Server level and the other at the database level. These two stages are implemented using Logins names and User accounts respectively. A valid login is required to connect to SQL Server and a valid user account is required to access a database. 3.6.1.
Login
A valid login name is required to connect to an SQL Server instance. A login could be: •
A Windows NT/2000 login that has been granted access to SQL Server
•
An SQL Server login, that is maintained within SQL Server
These login names are maintained within the master database. So, it is essential to backup the master database after adding new logins to SQL Server. 3.6.2.
User
A valid user account within a database is required to access that database. User accounts are specific to a database. All permissions and ownership of objects in the database are controlled by the user account. SQL Server logins are associated with these user accounts. A login can have associated users in different databases, but only one user per database. During a new connection request, SQL Server verifies the login name supplied, to make sure, that login is authorized to access SQL Server. This verification is called Authentication. SQL Server supports two authentication modes:
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Windows authentication mode:
With Windows authentication, you do not have to specify a login name and password, to connect to SQL Server. Instead, your access to SQL Server is controlled by your Windows NT/2000 account (or the group to which your account belongs to), that you used to login to the Windows operating system on the client computer/workstation. A DBA must first specify to SQL Server, all the Microsoft Windows NT/2000 accounts or groups that can connect to SQL Server Mixed mode:
Mixed mode allows users to connect using Windows authentication or SQL Server authentication. Your DBA must first create valid SQL Server login accounts and passwords. These are not related to your Microsoft Windows NT/2000 accounts. With this authentication mode, you must supply the SQL Server login and password when you connect to SQL Server. If you do not specify SQL Server login name and password, or request Windows Authentication, you will be authenticated using Windows Authentication. Point to note is that, whatever mode you configure your SQL Server to use, you can always login using Windows authentication. Windows authentication is the recommended security mode, as it is more secure and you don't have to send login names and passwords over the network. You should avoid mixed mode, unless you have a non-Windows NT/2000 environment or when your SQL Server is installed on Windows 95/98 or for backward compatibility with your existing applications. SQL Server's authentication mode can be changed using Enterprise Manager (Right click on the server name and click on Properties. Go to the Security tab). Authentication mode can also be changed using SQL DMO object model. Here is a list of helpful stored procedures for managing logins and users: sp_addlogin
Creates a new login that allows users to connect to SQL Server using SQL Server authentication
sp_grantlogin
Allows a Windows NT/2000 user account or group to connect to SQL Server using Windows authentication
sp_droplogin
Drops an SQL Server login
sp_revokelogin
Drops a Windows NT/2000 login/group from SQL Server
sp_denylogin
Prevents a Windows NT/2000 login/group from connecting to SQL Server
sp_password
Adds or changes the password for an SQL Server login
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sp_helplogins
Provides information about logins and their associated users in each database
sp_defaultdb
Changes the default database for a login
sp_grantdbaccess
Adds an associated user account in the current database for an SQL Server login or Windows NT/2000 login
sp_revokedbaccess Drops a user account from the current database sp_helpuser
Reports information about the Microsoft users and roles in the current database
Now let's talk about controlling access to objects within the database and managing permissions. Apart from managing permissions at the individual database user level, SQL Server 7.0/2000 implements permissions using roles. A role is nothing but a group to which individual logins/users can be added, so that the permissions can be applied to the group, instead of applying the permissions to all the individual logins/users. There are three types of roles in SQL Server 7.0/2000: • • •
Fixed server roles Fixed database roles Application roles 3.6.3. Fixed server roles
These are server-wide roles. Logins can be added to these roles to gain the associated administrative permissions of the role. Fixed server roles cannot be altered and new server roles cannot be created. Here are the fixed server roles and their associated permissions in SQL Server 2000: Fixed server role
Description
Sysadmin
Can perform any activity in SQL Server
serveradmin
Can set server-wide configuration options, shut down the server
setupadmin
Can manage linked servers and startup procedures
securityadmin
Can manage logins and CREATE DATABASE permissions, also read error logs and change passwords
processadmin
Can manage processes running in SQL Server
Dbcreator
Can create, alter, and drop databases
Diskadmin
Can manage disk files
Bulkadmin
Can execute BULK INSERT statements
Here is a list of stored procedures that are helpful in managing fixed server roles: sp_addsrvrolemember
Adds a login as a member of a fixed server role
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sp_dropsrvrolemember
Removes an SQL Server login, Windows user or group from a fixed server role
sp_helpsrvrole
Returns a list of the fixed server roles
sp_helpsrvrolemember Returns information about the members of fixed server roles sp_srvrolepermission 3.6.4.
Returns the permissions applied to a fixed server role
Fixed database roles
Each database has a set of fixed database roles, to which database users can be added. These fixed database roles are unique within the database. While the permissions of fixed database roles cannot be altered, new database roles can be created. Here are the fixed database roles and their associated permissions in SQL Server 2000: Fixed database role Description db_owner
Has all permissions in the database
db_accessadmin
Can add or remove user IDs
db_securityadmin
Can manage all permissions, object ownerships, roles and role memberships
db_ddladmin
Can issue ALL DDL, but cannot issue GRANT, REVOKE, or DENY statements
db_backupoperator Can issue DBCC, CHECKPOINT, and BACKUP statements db_datareader
Can select all data from any user table in the database
db_datawriter
Can modify any data in any user table in the database
db_denydatareader Cannot select any data from any user table in the database db_denydatawriter Cannot modify any data in any user table in the database
Here is a list of stored procedures that are helpful in managing fixed database roles: sp_addrole
Creates a new database role in the current database
sp_addrolemember
Adds a user to an existing database role in the current database
sp_dbfixedrolepermission Displays permissions for each fixed database role sp_droprole
Removes a database role from the current database
sp_helpdbfixedrole
Returns a list of fixed database roles
sp_helprole
Returns information about the roles in the current database
sp_helprolemember
Returns information about the members of a role in the current database
sp_droprolemember
Removes users from the specified role in the current d atabase
3.6.5.
Application roles
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Application roles are another way of implementing p ermissions. These are quite different from the server and database roles. After creating and assigning the required permissions to an application role, the client application needs to activate this role at run-time to get the permissions associated with that application role. Application roles simplify the job of DBAs, as they don't have to worry about managing permissions at individual user level. All they need to do is to create an application role and assign permissions to it. The application that is connecting to the database activates the application role and inherits the permissions associated with that role. Here are the characteristics of application roles: •
There are no built-in application roles
•
Application roles contain no members
•
•
•
Application roles need to be activated at run-time, by the application, using a password Application roles override standard permissions. For example, after activating the application role, the application will lose all the permissions associated with the login/user account used while connecting to SQL Server and gain the permissions associated with the application role Application roles are database specific. After activating an application role in a database, if that application wants to run a cross-database transaction, the other database must have a guest user account enabled
Here are the stored procedures that are required to manage application roles: sp_addapprole
Adds an application role in the current database
sp_approlepassword Changes the password of an application role in the current database sp_dropapprole
Drops an application role from the current database
sp_setapprole
Activates the permissions associated with an application role in the current database
Now that we discussed different kinds of roles, let's talk about granting/revoking permissions to/from database users and database roles and ap plication roles. The following T-SQL commands are used to manage permissions at the user and role level. •
•
•
GRANT: Grants the specific permission (Like SELECT, DELETE etc.) to the specified user or role in the current database REVOKE: Removes a previously granted or denied permission from a user or role in the current database DENY: Denies a specific permission to the specified user or role in the current database
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Using the above commands, permissions can be granted/denied/revoked to users/roles on all database objects. You can manage permissions at as low as the column level. Note: There is no way to manage permissions at the row level. That is, in a given table, you can't grant SELECT permission on a specific row to User1 and deny SELECT permission on another row to User2. This k ind of security can be implemented by using views and stored procedures effectively. Click here to read about row level security implementation in SQL Server databases. Just an FYI, Oracle has a feature called "Virtual Private Databases" (VPD) that allows DBAs to configure permissions at row level.
3.7.
Stored Procedures in SQL Server
Microsoft SQL Server provides the stored procedure mechanism to simplify the database development process by grouping Transact-SQL statements into manageable blocks. Benefits • Precompiled execution. SQL Server compiles each stored procedure once and then reutilizes the execution plan. This results in tremendous performance boosts when stored procedures are called repeatedly. • Reduced client/server traffic. If network bandwidth is a concern in your environment, you'll be happy to learn that stored procedures can reduce long SQL queries to a single line that is transmitted over the wire. • Efficient reuse of code and programming abstraction. Stored procedures can be used by multiple users and client programs. If you utilize them in a planned manner, you'll find the development cycle takes less time. • Enhanced security controls. You can grant users permission to execute a stored procedure independently of underlying table permissions. Structure Stored procedures are extremely similar to the constructs seen in other programming languages. They accept data in the form of input parameters that are specified at execution time. These input parameters (if implemented) are utilized in the execution of a series of statements that produce some result. This result is returned to the calling environment through the use of a recordset, output parameters and a return code. That may sound like a mouthful, but you'll find that stored procedures are actually quite simple. Let's take a look at a practical example. Example Assume we have the following table named Inventory: ID
Product
Warehouse
142 214 825 512 491
Green Beans Peas FL Corn NY Lima Beans Corn FL
NY 200 140 NY 80
Quantity
100
180
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85
This information is updated in real-time and warehouse managers are constantly checking the levels of products stored at their warehouse and available for shipment. In the past, each manager would run queries similar to the following: SELECT Product, Quantity FROM Inventory WHERE Warehouse = 'FL' This resulted in very inefficient performance at the SQL Server. Each time a warehouse manager executed the query, the database server was forced to recompile the query and execute it from scratch. It also required the warehouse manager to have knowledge of SQL and appropriate permissions to access the table information. We can simplify this process through the use of a stored procedure. Let's create a procedure called sp_GetInventory that retrieves the inventory levels for a given warehouse. Here's the SQL code:
CREATE PROCEDURE sp_GetInventory @location varchar(10) AS SELECT Product, Quantity FROM Inventory WHERE Warehouse = @location Our Florida warehouse manager can then access inventory levels by issuing the command EXECUTE sp_GetInventory 'FL' The New York warehouse manager can use the same stored procedure to access that area's inventory. EXECUTE sp_GetInventory 'NY' Granted, this is a simple example, but the benefits of abstraction can be seen here. The warehouse manager does not need to understand SQL or the inner workings of the procedure. From a performance perspective, the stored procedure will work wonders. The SQL Sever creates an execution plan once and then reutilizes it by plugging in the appropriate parameters at execution time. Now that you've learned the benefits of stored procedures, get out there and use them! Try a few examples and measure the performance enhancements achieved -- you'll be amazed!
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3.8. Performance considerations in TSQL 1. Consider using NOLOCK hint, while querying source data. This will avoid unnecessary locking at source and also avoid Refresh job failures due to locking 2. Use GROUP BY clause instead of DISTINCT 3. Make sure that the first column referred in the WHERE clause is indexed and, if this column is part of a composite index make sure that it is the first column of the composite index columns.It avoids Index/Table scans 4. Avoid using functions like LEFT, RIGHT, SUBSTRING in WHERE clause. These functions bypass the index usage. Instead look for alternatives like ‘LIKE’ 5. Use table variables instead of temporary tables while operating on less data. This reduces locking, logging resources and recompilations. 6. Use BETWEEN operator to search a range of values instead of the IN operator or a compound (col >= start) AND (col <= end) clause. Use SELECT e.Emp_Id FROM Employees e WHERE e.Emp_Id BETWEEN 1 and 10 Instead of SELECT e.Emp_Id FROM Employees e WHERE e.Emp_Id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) 7. Consider using UNION ALL instead of UNION.UNION will internally use DISTINCT where it is not the case with UNIONALL 8. Avoid using ISNULL function on NOT NULL columns wherever applicable. 9. Create Temporary tables out side transaction. 10. Make transactions as small as possible to avoid deadlocks. 11. General issues in a poor performing query •
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Some general issues that you could talk about would be: No indexes, table scans, missing or out of date statistics, blocking, excess recompilations of stored procedures, procedures and triggers without SET NOCOUNT ON, poorly written query with unnecessarily complicated joins, too much normalization, excess usage of cursors and temporary tables. Some of the tools/ways that help you troubleshooting performance problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET
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STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor, Graphical execution plan in Query Analyzer.
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Appendix A – Transaction Log Architecture
Every Microsoft® SQL Server™ 2000 database has a transaction log that records all transactions and the database modifications made by each transaction. This record of transactions and their modifications supports three operations: •
Recovery of individual transactions. If an application issues a ROLLBACK statement, or if SQL Server detects an error such as the loss of communication with a client, the log records are used to roll back the modifications made by an incomplete transaction.
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Recovery of all incomplete transactions when SQL Server is started. If a server running SQL Server fails, the databases may be left in a state where some modifications were never written from the buffer cache to the data files, and there may be some modifications from incomplete transactions in the data files. When a copy of SQL Server is started, it runs a recovery of each database. Every modification recorded in the log which may not have been written to the data files is rolled forward. Every incomplete transaction found in the transaction log is then rolled back to ensure the integrity of the database is preserved.
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Rolling a restored database forward to the point of failure. After the loss of a database, as is possible if a hard drive fails on a server that does not have RAID drives, you can restore the database to the point of failure. You first restore the last full or differential database backup, and then restore the sequence of transaction log backups to the point of failure. As you restore each log backup, SQL Server reapplies all the modifications recorded in the log to roll forward all the transactions. When the last log backup is restored, SQL Server then uses the log information to roll back all transactions that were not complete at that point.
The characteristics of the SQL Server 2000 transaction log are: •
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The transaction log is not implemented as a table but as a separate file or set of files in the database. The log cache is managed separately from the buffer cache for data pages, resulting in simple, fast, and robust code within the database engine. The format of log records and pages is not constrained to follow the format of data pages.
