How do you check what version of SQL Server for a database using TSQL?

Question

Try

SELECT @@VERSION 

or for SQL Server 2000 and above the following is easier to parse :)

SELECT SERVERPROPERTY('productversion')
     , SERVERPROPERTY('productlevel')
     , SERVERPROPERTY('edition')

From: http://support.microsoft.com/kb/321185

SELECT @@VERSION

I know this is an older post but I updated the code found in the link (which is dead as of 2013-12-03) mentioned in the answer posted by Matt Rogish:

DECLARE @ver nvarchar(128)
SET @ver = CAST(serverproperty('ProductVersion') AS nvarchar)
SET @ver = SUBSTRING(@ver, 1, CHARINDEX('.', @ver) - 1)

IF ( @ver = '7' )
   SELECT 'SQL Server 7'
ELSE IF ( @ver = '8' )
   SELECT 'SQL Server 2000'
ELSE IF ( @ver = '9' )
   SELECT 'SQL Server 2005'
ELSE IF ( @ver = '10' )
   SELECT 'SQL Server 2008/2008 R2'
ELSE IF ( @ver = '11' )
   SELECT 'SQL Server 2012'
ELSE IF ( @ver = '12' )
   SELECT 'SQL Server 2014'
ELSE IF ( @ver = '13' )
   SELECT 'SQL Server 2016'
ELSE IF ( @ver = '14' )
   SELECT 'SQL Server 2017'
ELSE
   SELECT 'Unsupported SQL Server Version'

For SQL Server 2000 and above, I prefer the following parsing of Joe's answer:

declare @sqlVers numeric(4,2)
select @sqlVers = left(cast(serverproperty('productversion') as varchar), 4)

Gives results as follows:

Result   Server Version
8.00     SQL 2000
9.00     SQL 2005
10.00    SQL 2008
10.50    SQL 2008R2
11.00    SQL 2012
12.00    SQL 2014

Basic list of version numbers here, or exhaustive list from Microsoft here.