PMA\libraries\DbQbe::_getLeftJoinColumnCandidatesBest PHP Method

    private function _getLeftJoinColumnCandidatesBest($search_tables, $where_clause_columns, $unique_columns, $index_columns)
    {
        // now we want to find the best.
        if (isset($unique_columns) && count($unique_columns) > 0) {
            $candidate_columns = $unique_columns;
            $needsort = 1;
            return array($candidate_columns, $needsort);
        } elseif (isset($index_columns) && count($index_columns) > 0) {
            $candidate_columns = $index_columns;
            $needsort = 1;
            return array($candidate_columns, $needsort);
        } elseif (isset($where_clause_columns) && count($where_clause_columns) > 0) {
            $candidate_columns = $where_clause_columns;
            $needsort = 0;
            return array($candidate_columns, $needsort);
        } else {
            $candidate_columns = $search_tables;
            $needsort = 0;
            return array($candidate_columns, $needsort);
        }
    }