ALTER DATABASE replaces sp_dbcmptlevel

ALTER DATABASE Compatibility Level (Transact-SQL)

Sets certain database behaviors to be compatible with the specified version of SQL Server. New in SQL Server 2008, the following ALTER DATABASE syntax replaces the sp_dbcmptlevel procedure for setting the database compatibility level. For other ALTER DATABASE options, see ALTER DATABASE (Transact-SQL).

ALTER DATABASE AdventureWorks
SET COMPATIBILITY_LEVEL = 100;
GO

vs

sp_dbcmptlevel AdventureWorks 100

Getting this error when trying to create an assembly from a DLL.

Determine current database compatibility level
DBCC CHECKDB

Checks the logical and physical integrity of all the objects in the specified database by performing the following operations:

• Runs DBCC CHECKALLOC on the database.
  
• Runs DBCC CHECKTABLE on every table and view in the database.
  
• Runs DBCC CHECKCATALOG on the database.
  
• Validates the contents of every indexed view in the database.
  
• Validates link-level consistency between table metadata and file system directories and files when storing varbinary(max) data in the file system using FILESTREAM.
  
• Validates the Service Broker data in the database.
  

This means that the DBCC CHECKALLOC, DBCC CHECKTABLE, or DBCC CHECKCATALOG commands do not have to be run separately from DBCC CHECKDB. For more detailed information about the checks that these commands perform, see the descriptions of these commands.