Understanding SQL Server Compatibility Level

Hello Dev, are you aware of the SQL Server compatibility level? In this article, we will explore this important concept and its significance in the world of database management. We will discuss the definition, usage, and benefits of compatibility level, as well as provide answers to frequently asked questions. So, let’s dive in!

What is SQL Server Compatibility Level?

Compatibility level refers to a database property that determines how a particular database engine version will behave when it encounters an instance of another engine version. In essence, it defines the degree of compatibility between the database and the engine.

For example, if you have a SQL Server 2012 database, it will work with a SQL Server 2014 engine in a backward compatibility mode. This is because the engine has to assume that certain features of the newer version will not work properly or at all with the older database. By setting the compatibility level, you can ensure that your database operates as intended with the engine version you are using.

Why is Compatibility Level Important?

Compatibility level is crucial in ensuring that database applications run smoothly and efficiently. It helps minimize compatibility issues between different versions of SQL Server engine as well as ensure that features and functions are supported by the database engine before being used in a production environment.

Additionally, setting the compatibility level allows you to test new versions of SQL Server without putting the data at risk. If you migrate a database to a new version and set its compatibility level to an older version, you can test the new engine features without any loss of data.

How to Set SQL Server Compatibility Level?

Setting the compatibility level for a database is simple. You can do this via SQL Server Management Studio (SSMS) or Transact-SQL (T-SQL). Let’s take a look at both methods:

Via SQL Server Management Studio

1. Connect to the SQL Server instance using SSMS
2. Select the database for which you want to set the compatibility level
3. Right-click on the database and select ‘Properties’
4. Go to the ‘Options’ page and select the desired compatibility level from the dropdown
5. Click ‘OK’ to save changes

Via Transact-SQL

You can also use Transact-SQL to set the compatibility level. Make sure you have appropriate permissions to perform the operation. Here’s an example of how to set the compatibility level to 2016:

ALTER DATABASE [dbname] SET COMPATIBILITY_LEVEL = 130

Replace [dbname] with the name of your database and 130 with the compatibility level you want to set.

Compatibility Levels for Different Versions of SQL Server

The compatibility level is version-specific and can be set to any integer value between 80 and the current version of SQL Server.

Compatibility Level	SQL Server Version
80	SQL Server 2000
90	SQL Server 2005
100	SQL Server 2008 and 2008 R2
110	SQL Server 2012
120	SQL Server 2014
130	SQL Server 2016 and later

Frequently Asked Questions

1. What happens if I set my compatibility level to a version that is not supported by my SQL Server engine?

If you set the compatibility level to a version that is not supported by your engine, the database will not be able to function properly, and you may encounter errors. It’s important to ensure that your compatibility level matches your engine version.

2. Can I change the compatibility level of a database without restarting the SQL Server engine?

Yes, you can change the compatibility level of a database without restarting the SQL Server engine. However, any queries that were running at the time of the change may be affected.

3. Is it possible to run a database on an older engine version than the compatibility level?

No, it is not advisable to run a database on an older engine version than the compatibility level. Doing so can lead to data loss or corruption due to unsupported features.

4. How do I determine the compatibility level of a database?

You can determine the compatibility level of a database by running the following T-SQL command:

SELECT compatibility_level FROM sys.databases WHERE name = 'dbname'

Replace dbname with the name of your database.

5. How often should I change the compatibility level?

The compatibility level should be changed only when necessary, such as when you are upgrading your SQL Server engine version. Changing it too frequently can lead to compatibility issues and may result in data loss or corruption.

Conclusion

Compatibility level is a critical concept in SQL Server database management. It helps ensure that your database runs smoothly and efficiently while minimizing compatibility issues between different versions of the engine. By understanding and properly setting the compatibility level, you can optimize the performance of your SQL Server database and keep your data safe and secure.