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SQL SERVER INTERVIEW QUESTIONS 2014 BOOKLET -8 By Mr.J.Venkatesan Prabu - Managing Director of Kaashiv Infotech

            
      SQL SERVER INTERVIEW QUESTIONS 2014- SET 8 By 
"Mr.J.Venkatesan Prabu" 

KAASHIV INFOTECH

     [ The  Asia, India & Tamil Nadu Book Of  Record Holders ]


                                                       
    SQL Server Interview Questions 2014
SQL  SERVER –Booklet 8
-         Gives you the interview tips for SQL Server

 SQL SERVER INTERVIEW QUESTIONS WITH ANSWERS 

1. What is the difference between UNION and UNION ALL?
  1. UNION The UNION command is used to select related information from two tables, much like the JOIN command. However, when using the UNION command all selected columns need to be of the same data type. With UNION, only distinct values are selected.

  3. UNION ALL The UNION ALL command is equal to the UNION command, except that UNION ALL selects all values.
The difference between Union and Union all is that Union all will not eliminate duplicate rows, instead it just pulls all rows from all tables fitting your query specifics and combines them into a table.

2. What is B-Tree?

The database server uses a B-tree structure to organize index information. B-Tree generally has following types of index pages or nodes:
  1. root node: A root node contains node pointers to branch nodes which can be only one.
  2. branch node: A branch node contains pointers to leaf nodes or other branch nodes which can be two or more.
  3. leaf nodes: A leaf node contains index items and horizontal pointers to other leaf nodes which can be many.
3. What is the difference between lock, block and deadlock?

Lock: DB engine locks the rows/page/table to access the data which is worked upon according to the query.
Block: When one process blocks the resources of another process then blocking happens. Blocking can be identified by using
SELECT * FROM sys.dm_exec_requests where blocked <> 0
SELECT * FROM master..sysprocesses where blocked <> 0
Deadlock: When something happens as follows: Error 1205 is reported by SQL Server for deadlock.

4.What is the meaning of lock escalation and why/how to stop this?

When the DB engine would try to lock page first and then it escalates locks to page and then table. If we understand that whole table would be locked for the processing thenn this is better to use TABLOCK hint and get complete table blocked. This is a nice way to avoid the wastage of sql server DB engine processing for lock escalation. Somewhere you may also need to use TABLOCKX when you want an exclusive lock on the table in the query.
5. How to truncate the log in sql server 2008?
BACKUP LOG TestDB WITH TRUNCATE_ONLY is gone. SQL server doesn’t allow you to truncate the log now otherwise whole purpose of a DB is defeated. Read articlehttp://mssqlcorruptiontackle.blogspot.com/2010/12/mssql-server-dbcc-loginfo-status-2-log.html to surprise interviewer with your answer. You have to make sure whether you need log or not. If you don’t need log then have the recovery model simple instead of full. If you don’t want the log to be accumulated in some particular bulk logging then change the recovery model BULK LOGGED for that duration and take one tlog backup just before and after this change. I shall discuss this later in my later blog. BACKUP LOG command backs up the t-log and frees the space in the log file.
6. What changes in the front end code is needed if mirroring is implemented for the high availability?
You need to add only FAILOVER PARTNER information in your front end code. “Data Source=ServerA;Failover Partner=ServerB;Initial Catalog=AdventureWorks;Integrated Security=True;”.
7. Where does the copy job runs in the logshipping… Primary or secondary?
Secondary server. This question is basically asked to find out whether you have a handson work on logshipping or not. I came through many cases when candidates have mentioned logshipping experience in many projects and they can’t answer this question. I never selected any candidate if he/she don’t answer these kind of small questions.
8. What are the ways to find what code is running for any spid?
Well there are many ways to do this.
1. find the spid which you want to analyze. An spid is assigned as soon as a client connection is established with the SQL server. To find the spid you can run any of the following command:
a) SP_WHO2 ‘ACTIVE’ — This will give you only active spids.
b) SELECT * FROM sys.dm_exec_requests  
2. Get the spid from above two queries and use any of the following query to get what is happening behind that spid.
a) dbcc inputbuffer()
b) sql2005 and sql2008 – SELECT * FROM sys.dm_exec_sql_text()
c) sql2005 and sql2008 – SELECT * FROM fn_get_sql()
9. When you get following error? Error 3154: The backup set holds a backup of a database other than the existing database.
The error comes when you are trying to restore the DB which already exists. Use WITH REPLACE option to restore the DB with a different name.
 Yes and No. This is tricky question. If you are using repair option with CHECKDB then you have to have the DB in single user mode. Following is the method to have your DB in a single user mode.
Use master
go
sp_dboption dbname, single, true
Following is the error which you get when you run the DBCC CHECKDB with repair option w\o having the DB in single user mode.
The same is true for DBCC CHECKDB also.
11. How to view the error log for any specific instance?
There are many ways but I prefer following method. Take a scenario when you want to find the error log when the DB was put in a single user mode.
CREATE TABLE #Errorlog (Logdate Datetime, Processinfo VARCHAR(20),Text VARCHAR(2000))
INSERT INTO #Errorlog
EXEC xp_readerrorlog
SELECT * FROM #Errorlog
WHERE Text Like ‘%SINGLE%USER%’

12. What does the NOLOCK query hint do?

Table hints allow you to override the default behavior of the query optimizer for statements. They are specified in the FROM clause of the statement. While overriding the query optimizer is not always suggested, it can be useful when many users or processes are touching data. The NOLOCK query hint is a good example because it allows you to read data regardless of who else is working with the data; that is, it allows a dirty read of data -- you read data no matter if other users are manipulating it. A hint like NOLOCK increases concurrency with large data stores.
SELECT * FROM table_name (NOLOCK)
Microsoft advises against using NOLOCK, as it is being replaced by the READUNCOMMITTED query hint. There are lots more query hints with plenty of information online.
13.  What are the new features in SQL Server 2005 when compared to SQL Server 2000?
There are quite a lot of changes and enhancements in SQL Server 2005. Few of them are listed here :
§  Database Partitioning
§  Dynamic Management Views
§  System Catalog Views
§  Resource Database
§  Database Snapshots
§  SQL Server Integration Services
§  Support for Analysis Services on a a Failover Cluster.
§  Profiler being able to trace the MDX queries of the Analysis Server.
§  Peer-toPeer Replication
§  Database Mirroring

14. What are the High-Availability solutions in SQL Server and differentiate them briefly.
§  Failover Clustering, Database Mirroring, Log Shipping and Replication are the High-Availability features available in SQL Server. I would recommend reading this blog of mine which explains the differences between these 4 features. Comparing the High Availability Features in SQL Server 2005

15. How do you troubleshoot errors in a SQL Server Agent Job?
§  Inside SSMS, in Object explorer under SQL Server Agent look for Job Activity Monitor. The job activity monitor displays the current status of all the jobs on the instance. Choose the particular job which failed, right click and choose view history from the drop down menu. The execution history of the job is displayed and you may choose the execution time (if the job failed multiple times during the same day). There would information such as the time it took to execute that Job and details about the error occurred.


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My T-SQL Gallery @code.msdn.microsoft


Created my own T-SQL Gallery in Microsoft site. Do visit the same and share your feedback,

http://code.msdn.microsoft.com/VenkatSQLSample/Thread/List.aspx

Thanks and Regards,
Venkatesan Prabu .J

SQL Server Interview questions - Part 1

What is the significance of NULL value and why should we avoid permitting null values?
Null means no entry has been made. It implies that the value is either unknown or undefined.We should avoid permitting null values because Column with NULL values can't have PRIMARY KEY constraints. Certain calculations can be inaccurate if NULL columns are involved.

What is SQL whats its uses and its component ?
The Structured Query Language (SQL) is foundation for all relational database systems. Most of the large-scale databases use the SQL to define all user and administrator interactions. It enable us to retrieve the data from based on our exact requirement. We will be given a flexibility to store the data in our own format.


The DML component of SQL comprises four basic statements:
* SELECT to get rows from tables
* UPDATE to update the rows of tables
* DELETE to remove rows from tables
* INSERT to add new rows to tables

What is DTS in SQL Server ?
Data Transformation Services is used to transfer the data from one source to our required destination. Considering am having some data in sql server and I need to transfer the data to Excel destination. Its highly possible with dialogue based tool called Data Transformation services. More customization can be achieved using SSIS. A specialized tool used to do such migration works.


What is the difference between SQL and Pl/Sql ?

Straight forward. SQL is a single statement to finish up our work.Considering, I need some data from a particular table. “Select * from table” will fetch the necessary information. Where as I need to do some row by row processing. In that case, we need to go for Procedural Logic / SQL.

What is the significance of NULL value and why should we avoid permitting null values?
Null means no entry has been made. It implies that the value is either unknown or undefined.We should avoid permitting null values because Column with NULL values can't have PRIMARY KEY constraints. Certain calculations can be inaccurate if NULL columns are involved.

Difference between primary key and Unique key?
Both constraints will share a common property called uniqueness. The data in the column should be unique. The basic difference is,
· Primary key won’t allow null value. Whereas, unique key will accept null value but only one null value.
· On creating primary key, it will automatically format the data inturn creates clustered index on the table. Whereas, this characteristics is not associated with unique key.
· Only one primary key can be created for the table. Any number of Unique key can be created for the table.

Select Statement in SQL Server

Select Statement in SQL Server

String Functions in sql server

String Functions in sql server
Substring/Len/replace/Ltrim/Rtrim

SQL Server Interview Question - Part 2

What is normalization?

Normalization is the basic concept used in designing a database. Its nothing but, an advise given to the database to have minimal repetition of data, highly structured, highly secured, easy to retrieve. In high level definition, the Process of organizing data into tables is referred to as normalization.


What is a stored procedure:
Stored procedures are precompiled T-SQL statements combined to perform a single task of several tasks. Its basically like a Macro so when you invoke the Stored procedure, you actually run a set of statements. As, its precompiled statement, execution of Stored procedure is compatatively high when compared to an ordinary T-SQL statement.


What is the difference between UNION ALL Statement and UNION ?
The main difference between UNION ALL statement and UNION is UNION All statement is much faster than UNION,the reason behind this is that because UNION ALL statement does not look for duplicate rows, but on the other hand UNION statement does look for duplicate rows, whether or not they exist.

Example for Stored Procedure?
They are three kinds of stored procedures,1.System stored procedure – Start with sp_2. User defined stored procedure – SP created by the user.3. Extended stored procedure – SP used to invoke a process in the external systems.Example for system stored proceduresp_helpdb - Database and its propertiessp_who2 – Gives details about the current user connected to your system. sp_renamedb – Enable you to rename your database


What is a trigger?

Triggers are precompiled statements similar to Stored Procedure. It will automatically invoke for a particular operation. Triggers are basically used to implement business rules.


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 specfic users to see only 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.


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.


What are the types of indexes available with SQL Server?

There are basically two types of indexes that we use with the SQL ServerClustered -

1. It will format the entire table, inturn physically sort the table.

2. Only one clustered index can be created for a table.

3. Data will be located in the leaf level.

4. By default, primary key will create clustered index on the table.

Non-Clustered Index

1. It wont touch the structure of the table.

2. It forms an index table as reference to the exact data.

3. A reference to the data will be located in the leaf level.

4. For a table, we can create 249 non clustered index.

Happy Learning!!!
Regards,
Venkatesan Prabu .J

SQL Interview question

Extent Vs Page?

Pages are low level unit to store the exact data in sql server. Basically, the data will be stored in the mdf, ldf, ndf files. Inturn, pages are logical units available in sql server.The size of the page is 8KB.

Eight consecutive pages will form an extent 8 * 8KB = 64KB.

Thus I/O level operation will be happening at pages level.The pages will hold a template information at the start of each page (header of the page).

They are,

1. page number,

2. page type,

3. the amount of free space on the page,

4. the allocation unit ID of the object that owns the page.

Extents will be classifed into two types,

1. Uniform extents

2. Mixed extents

Uniform Extents:It occupied or used by a single object. Inturn, a single object will hold the entire 8 pages.Mixed

Extents:Mulitple objects will use the same extent. SQL Server will allow a max of eight objects to use a shared extent.

Property of SQL Server :Initally if an object is created, sql server will allocate the object to the mixed extent and once if the size reaches 8 pages and more... immediately, a new uniform extent will be provided for that particular object.

Herecomes, our fragmentation and reindexing concepts.



Best Joke - Enjoy it

Best Joke - Enjoy it