Transact-SQL provides the sp_dbcmptlevel stored procedure that sets certain database behaviors to be compatible with the specified earlier version of Microsoft® SQL Server™.
A special rule applies to the relationship among the database compatibility level option, the concat null yields null database option, and the CONCAT_NULL_YIELDS_NULL SET option. The settings of concat null yields null and CONCAT_NULL_YIELDS_NULL are ignored when the value of compatibility level is for a release earlier than 7.0.
The compatibility level affects the behaviors in the specified database, not the entire server. For more information, see sp_dbcmptlevel.