Server configuration: clr enabled
Applies to: 
SQL Server
Use the clr enabled option to specify whether SQL Server can run user assemblies. The clr enabled option provides the following values:
| Value | Description |
|---|---|
0 |
Assembly execution not allowed on SQL Server. |
1 |
Assembly execution allowed on SQL Server. |
For WOW64 only: restart WOW64 servers to apply these changes. No restart is required for other server types.
When you run RECONFIGURE, and the run value of the clr enabled option is changed from 1 to 0, all application domains containing user assemblies are immediately unloaded.
Limitations
Common language runtime (CLR) execution isn't supported under lightweight pooling
Disable one of two options: clr enabled or lightweight pooling. Features that rely upon CLR and that don't work properly in fiber mode include the hierarchyid data type, the FORMAT function, replication, and Policy-Based Management. For more information, see Server configuration: lightweight pooling.
Though the clr enabled configuration option is enabled in Azure SQL Database, developing CLR user functions aren't supported in Azure SQL Database.
Code access security no longer supported
CLR uses Code Access Security (CAS) in the .NET Framework, which is no longer supported as a security boundary. A CLR assembly created with PERMISSION_SET = SAFE might be able to access external system resources, call unmanaged code, and acquire sysadmin privileges. In SQL Server 2017 (14.x) and later versions, the sp_configure option, clr strict security, enhances the security of CLR assemblies. clr strict security is enabled by default, and treats SAFE and EXTERNAL_ACCESS assemblies as if they were marked UNSAFE. The clr strict security option can be disabled for backward compatibility, but isn't recommended.
We recommend that you sign all assemblies by a certificate or asymmetric key, with a corresponding login that has been granted UNSAFE ASSEMBLY permission in the master database. SQL Server administrators can also add assemblies to a list of assemblies, which the Database Engine should trust. For more information, see sys.sp_add_trusted_assembly.
Examples
The following example first displays the current setting of the clr enabled option and then enables the option by setting the option value to 1. To disable the option, set the value to 0.
EXEC sp_configure 'clr enabled';
EXEC sp_configure 'clr enabled' , '1';
RECONFIGURE;