Error - Exclusive access could not be obtained because the database is in use

Question

I am actually trying to make a script (in Sql Server 2008) to restore one database from one backup file. I made the following code and I am getting an error -
Msg 3101, Level 16, State 1, Line 3
Exclusive access could not be obtained because
the database is in use.
Msg 3013, Level 16, State 1, Line 3
RESTORE DATABASE is terminating abnormally.
How do I fix this problem ?
IF DB_ID('AdventureWorksDW') IS NOT NULL
BEGIN
RESTORE DATABASE [AdventureWorksDW]
FILE = N'AdventureWorksDW_Data'
FROM
DISK = N'C:\Program Files\Microsoft SQL Server\
MSSQL10_50.SS2008\MSSQL\Backup\AdventureWorksDW.bak'
WITH FILE = 1,
MOVE N'AdventureWorksDW_Data'
TO N'C:\Program Files\Microsoft SQL Server\
MSSQL10_50.SS2008\MSSQL\DATA\AdventureWorksDW.mdf',
MOVE N'AdventureWorksDW_Log'
TO N'C:\Program Files\Microsoft SQL Server\
MSSQL10_50.SS2008\MSSQL\DATA\AdventureWorksDW_0.LDF',
NOUNLOAD, STATS = 10
END

Answer 1

Check, if there are existing connections to the database you are restoring by following command
select spid from sys.sysprocesses where dbid = db_id('AdventureWorksDW')
if you see any existing connections then kill them by issuing KILL command Syntax for kill is
KILL <SPID>
once you see there are no more connections then 
Use mastergoIF DB_ID('AdventureWorksDW') IS NOT NULL
BEGIN
RESTORE DATABASE [AdventureWorksDW]
FILE = N'AdventureWorksDW_Data'
FROM
DISK = N'C:\Program Files\Microsoft SQL Server\
MSSQL10_50.SS2008\MSSQL\Backup\AdventureWorksDW.bak'
WITH FILE = 1,
MOVE N'AdventureWorksDW_Data'
TO N'C:\Program Files\Microsoft SQL Server\
MSSQL10_50.SS2008\MSSQL\DATA\AdventureWorksDW.mdf',
MOVE N'AdventureWorksDW_Log'
TO N'C:\Program Files\Microsoft SQL Server\
MSSQL10_50.SS2008\MSSQL\DATA\AdventureWorksDW_0.LDF',
NOUNLOAD, STATS = 10
END
Mark as answer, if it works.