SQL Server

What is SQL Server?

Microsoft SQL Server is Relational database management system (RDBMS) developed and owned by Microsoft. It is a software product whose primary function is to store and retrieve data as requested by other software applications, be it those on the same computer or those running on another computer across a network (including the Internet). There are at least a dozen different editions of Microsoft SQL Server aimed at different audiences and for different workloads (ranging from small applications that store and retrieve data on the same computer, to millions of users and computers that access huge amounts of data from the Internet at the same time).

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SQL Server

SQL Server 2012 Editions:

Enterprise Edition

Standard Edition

Compact Edition

Express Edition

Web Edition

Free Editions of SQL Server:

You can download free edition of SQL Server with these links

SQL Server 2012 Express Edition

Microsoft SQL Server 2008 R2 Express Edition

Microsoft SQL Server 2005 Express Edition

Application to manage SQL Server:

Microsoft provides a software application named SQL Server Management Studio . This provides an Editor with intelligence and graphical management tools. 

DBCC Commands for SQL Server

DBCC Commands:

DBCC commands are most useful for performance and troubleshooting.
The DBCC Commands are used in Maintenance, Informational use, Validation on a database, index, or file group. Theses commands are helpful to check physical and logical consistency of database. Some DBCC statements fix errors automatically. Here I am showing some commands that are frequently used.

Command	Description	Level	When to Check
DBCC SQLPERF(logspace)	--To see transaction log size of each database on Server.	Server Level	Weekly
DBCC SHOWFILESTATS	--Show Total Extents and used extents for database	Database Level	Weekly
DBCC CHECKCATALOG	--Checks for catalog/tables consistency within the specified database	Database Level	Weekly
DBCC CHECKCONSTRAINTS	--Checks the integrity of a specified constraint or all constraints on a specified table in the current database	Database Level	When you suspect that there are rows in your tables that do not meet the constraints/rules.
DBCC CHECKALLOC	-- checks page usage and allocation in the database.	Database Level	if allocation errors are found for the database
DBCC CHECKTABLE(tablename)	--It verifies index and data page links, index sort order, page pointers, index pointers, data page integrity, and page offsets on table.	Table level	Whenever required.
DBCC CHECKIDENT(tablename)	--Checking identity information,return current identity value of specified table	Table Level	Whenever required.
DBCC DBREINDEX(tablename)	-- rebuilds an index for a table or all indexes defined for a table.	Table level	(should not used rather use ALTER INDEX command)
DBCC INDEXDEFRAG (databasename, tablename,indexname)	--defragment clustered and nonclustered indexes on tables and views	Table/View Level	(Should not use, Replacement is ALTER INDEX ... REORGANISE)
SELECT request_id FROM sys.dm_exec_requests WHERE session_id = @@spid;	--returns request_id
DBCC INPUTBUFFER(sessionid)	--to view the last statement sent by the client connection to SQL Server	Database level	Whenever required
DBCC SHRINKDATABASE(databasename)	--Shrinks the size of the data and log files in the specified database	Database Level	Avoid executing this command during busy periods in production
DBCC SHRINKFILE(file_id) Use exec sp_helpfile  to know filename,fileid,filegroup,size	--allows you to shrink the size of individual data and log files	Database level	Avoid, as in most cases the database will just regrow and shrinking data files causes fragmentation.
DBCC TRACEOFF	--used to disable tracing	Server Level
DBCC TRACEON	--used to enable tracing	Server Level
DBCC TRACESTATUS	--used to know trace status with TraceFlag,Status,Global,Session	Server Level
DBCC USEROPTIONS	--Returns the SET options active (set) for the current connection	Server Level	Whenever required

Frequently asked Scripts during Interviews

1. Select no of Months between two dates:

SELECT

    DATEDIFF(MONTH, '4/1/2011', '01/23/2013') +

    CASE

        WHEN DAY('4/1/2011') < DAY('01/23/2013')

        THEN 1

        ELSE 0

    END

Output:

----------------

22

2. What will be the output of following script

CREATE TABLE dbo.t1

(

 id INT NOT NULL IDENTITY (1, 1),

 name VARCHAR(100)

);

INSERT  INTO dbo.t1

        (name)

VALUES  ('sonu');

DBCC CHECKIDENT ('dbo.t1', RESEED, 24);

INSERT  INTO dbo.t1

        (name)

VALUES  ('queryingsql');

SELECT  id

FROM    dbo.t1;

Output:

---------------------------

1

25

3. Create a query that display the Emp name and indicate the amounts of their annual salaries with asterisks. Each asterisk signifies a thousand rupees. Sort the data in descending order of salary. As for example if Emp name sonu have salary 11000. Then output should be Sonu***********.

select FirstName+SUBSTRING('****************************

********************************************************

********************************************************

********************************************************

*************************************************',1,ROUND(salary/1000,0))

    as Employee_and_salary ,salary from Employee order by salary desc;

Output:

---------------------------------------------------------------

Employee_and_salary    salary

sonu***********                         11000

mohit**********                         10000

mohit**********                         10000

monu*********                            9000

More script coming soon...........