Upgrading SQL Server databases and changing compatibility levels

Problem
When upgrading databases from an older version of SQL Server using either the backup and restore method or detach and attach method the compatibility level does not automatically change and therefore your databases still act as though they are running using an earlier version of SQL Server.  From an overall standpoint this is not a major problem, but there are certain features that you will not be able to take advantage of unless your database compatibly level is changed.  This tip will show you how to check the current compatibly level, how to change the compatibly level and also some of the differences between earlier versions and SQL Server 2005.

SolutionThe first thing that you need to do is to check the compatibility level that your database is running under.  As mentioned above any database that is upgraded using the backup and restore or detach and attach method will not change the compatibly level automatically, so you will need to check each database and make the change.

Although SQL Server has changed its naming convention to SQL Server 2000, 2005 and soon to be released 2008 the internal version numbers still remain.  Here is a list of the compatibly levels (versions) that you will see:

• 60 = SQL Server 6.0
• 65 = SQL Server 6.5
• 70 = SQL Server 7.0
• 80 = SQL Server 2000
• 90 = SQL Server 2005

---

Identifying Compatibly Level

To check the compatibility level of your databases you can use one of these methods:

Using SQL Server Management Studio, right click on the database, select "Properties" and look at the "Options" page for each database as the following image shows:

Another option is to use sp_helpdb so you can get the information for all databases at once:

EXEC sp_helpdb

Or select directly from the sys.databases catalog to get the information for all databases.

SELECT * FROM sys.databases

---

Compatibly Level for New Databases

When issuing a CREATE DATABASE statement there is not a way to select which compatibility level you want to use.  The compatibility level that is used is the compatibility level of your model database.

Here is a sample CREATE DATABASE command, but there is not an option to change the compatibility level.

CREATE DATABASE [test] ON PRIMARY  ( NAME = N'test', FILENAME = N'Z:\SQLData\test.mdf' , SIZE = 2048KB , FILEGROWTH = 1024KB ) LOG ON  ( NAME = N'test_log', FILENAME = N'Y:\SQLData\test3_log.ldf' , SIZE = 3072KB , FILEGROWTH = 10%) GO

When creating a database using SQL Server Management Studio you have the ability to change the compatibility level on the "Options" tab such as follows:

If we use the "Script" option we can see that SQL Server issues the CREATE DATABASE statement and then issues "sp_dbcmptlevel" to set the database compatibility level to 80 as shown below.

CREATE DATABASE [test] ON PRIMARY  ( NAME = N'test', FILENAME = N'Z:\SQLData\test.mdf' , SIZE = 2048KB , FILEGROWTH = 1024KB ) LOG ON  ( NAME = N'test_log', FILENAME = N'Y:\SQLData\test3_log.ldf' , SIZE = 3072KB , FILEGROWTH = 10%) GO EXEC dbo.sp_dbcmptlevel @dbname=N'test', @new_cmptlevel=80 GO

---

Changing Compatibility Level

So once you have identified the compatibility level of your database and know what you want to change it to you can use the sp_dbcmptlevel system stored procedure to make the change.  The command has the following syntax:

sp_dbcmptlevel [ [ @dbname = ] name ]  [ , [ @new_cmptlevel = ] version ]--to change to level 80 dbo.sp_dbcmptlevel @dbname=N'test', @new_cmptlevel=80 --to change to level 90 dbo.sp_dbcmptlevel @dbname=N'test', @new_cmptlevel=90 --or sp_dbcmptlevel 'test', '80' sp_dbcmptlevel 'test', '90'

---

Differences

There are several differences on how compatibly levels affect your database operations.  SQL Server Books Online has a list of these differences and the following list shows you a few of these items:

Compatibility level setting of 80 or earlier	Compatibility level setting of 90	Possibility of impact
For locking hints in the FROM clause, the WITH keyword is always optional.	With some exceptions, table hints are supported in the FROM clause only when the hints are specified with the WITH keyword. For more information, see FROM (Transact-SQL).	High
The *= and =* operators for outer join are supported with a warning message.	These operators are not supported; the OUTER JOIN keyword should be used.	High
SET XACT_ABORT OFF is allowed inside a trigger.	SET XACT_ABORT OFF is not allowed inside a trigger.	Medium

(Source: SQL Server 2005 Books Online)  For a complete list of these items look here:

In addition, each new compatibility level offers a new list of reserved keywords.  Here is a list of the new keywords for SQL Server 2005.

Compatibility level setting	Reserved keywords
90	PIVOT, UNPIVOT, REVERT, TABLESAMPLE
80	COLLATE, FUNCTION, OPENXML
70	BACKUP, CONTAINS, CONTAINSTABLE, DENY, FREETEXT, FREETEXTTABLE, PERCENT, RESTORE, ROWGUIDCOL, TOP
65	AUTHORIZATION, CASCADE, CROSS, DISTRIBUTED, ESCAPE, FULL, INNER, JOIN, LEFT, OUTER, PRIVILEGES, RESTRICT, RIGHT, SCHEMA, WORK

(Source: SQL Server 2005 Books Online)

If one of these keywords is being used and your database is set to this compatibly level the commands will fail.  To get around this you could put the keyword in either square brackets ([ ]) or use quotation marks (" ") such as [PIVOT] or "PIVOT".

---

Summary

The compatibly level setting is used by SQL Server to determine how certain new features should be handled.  This was setup so you could migrate your databases to a later release of SQL Server without having to worry about the application breaking.  This setting can be changed forward and backwards if needed, so if you do change your compatibly level and find that there are problems you can set the value back again until you resolve all of the issues that you may be facing during the upgrade.

In addition, there are certain features that only work if the database is set to the latest compatibly level, therefore to get all of the benefits of the version of SQL Server you are running you need to make sure you are using the latest compatibly level.

 Source Collcted from MSSQLTIPS.COM