Manual:$wgSQLMode

From Linux Web Expert

<translate> MySQL-specific</translate>: $wgSQLMode
Value for the MySQL sql_mode parameter
<translate> Introduced in version:</translate>1.17.0 (r68558)
<translate> Removed in version:</translate><translate> still in use</translate>
<translate> Allowed values:</translate>(string) or null
<translate> Default value:</translate>''

Details

If this setting is not null, the MySQL server is sent the SQL query SET sql_mode = "$wgSQLMode". See the MySQL documentation for more details.

The default is null, which means that the query to set sql_mode is not issued. This can be used to skip the setting for performance reasons and assume the database admin (DBA) has done their best job.