Thread:Project:Support desk/SELECT DISTINCT for a query

How to I add the condition 'DISTINCT' to the following query: $all_res = $dbr->select(				'categorylinks',                                  // $table				array( 'cl_to', 'cl_from' ),            // $vars (columns of the table)				array('cl_to NOT IN'. $categories), 				__METHOD__,                                   // $fname = 'Database::select',				array( 'ORDER BY' => 'cl_from ASC' ) 			);