Manual:$wgShowSQLErrors

Debug/logging: $wgShowSQLErrors
Whether to show SQL errors on "we're sorry, but there has been a database error" pages.
Introduced in version:	1.4.0 (r7376)
Removed in version:	still in use
Allowed values:	(boolean)
Default value:	false

Other settings: Alphabetical | By Function

When set to false (default) any database error message will also say "(SQL query hidden)" rather than showing the SQL which caused the error. You will then only see "A database query error has occurred. This may indicate a bug in the software.". Set $wgShowSQLErrors to true to see the actual query, which caused the error.

Details

Clearly showing the SQL will aid in debugging in the event of a database error, however...

• Showing SQL to all users, will give crackers some clues about the database structure of your website, and might help them find security weaknesses.
• SQL database errors are not supposed to occur during any normal MediaWiki operation, and so with luck you will never need to improve the error information
• If you receive the error internal_api_error_DBQueryError from the API, enabling this setting will display a more descriptive error message in the info field than the default Database query error.

If you do see an error including "(SQL query hidden)", it can be useful to set this to $wgShowSQLErrors = true; temporarily.

This variable replaces $wgIgnoreSQLErrors, which should no longer be used.