PMA\libraries\DbQbe::_getMasterTable PHP Method

    private function _getMasterTable($search_tables, $search_columns, $where_clause_columns, $where_clause_tables)
    {
        if (count($where_clause_tables) == 1) {
            // If there is exactly one column that has a decent where-clause
            // we will just use this
            $master = key($where_clause_tables);
            return $master;
        }
        // Now let's find out which of the tables has an index
        // (When the control user is the same as the normal user
        // because he is using one of his databases as pmadb,
        // the last db selected is not always the one where we need to work)
        $candidate_columns = $this->_getLeftJoinColumnCandidates($search_tables, $search_columns, $where_clause_columns);
        // Generally, we need to display all the rows of foreign (referenced)
        // table, whether they have any matching row in child table or not.
        // So we select candidate tables which are foreign tables.
        $foreign_tables = array();
        foreach ($candidate_columns as $one_table) {
            $foreigners = PMA_getForeigners($this->_db, $one_table);
            foreach ($foreigners as $key => $foreigner) {
                if ($key != 'foreign_keys_data') {
                    if (in_array($foreigner['foreign_table'], $candidate_columns)) {
                        $foreign_tables[$foreigner['foreign_table']] = $foreigner['foreign_table'];
                    }
                    continue;
                }
                foreach ($foreigner as $one_key) {
                    if (in_array($one_key['ref_table_name'], $candidate_columns)) {
                        $foreign_tables[$one_key['ref_table_name']] = $one_key['ref_table_name'];
                    }
                }
            }
        }
        if (count($foreign_tables)) {
            $candidate_columns = $foreign_tables;
        }
        // If our array of candidates has more than one member we'll just
        // find the smallest table.
        // Of course the actual query would be faster if we check for
        // the Criteria which gives the smallest result set in its table,
        // but it would take too much time to check this
        if (!(count($candidate_columns) > 1)) {
            // Only one single candidate
            return reset($candidate_columns);
        }
        // Of course we only want to check each table once
        $checked_tables = $candidate_columns;
        $tsize = array();
        $maxsize = -1;
        $result = '';
        foreach ($candidate_columns as $table) {
            if ($checked_tables[$table] != 1) {
                $_table = new Table($table, $this->_db);
                $tsize[$table] = $_table->countRecords();
                $checked_tables[$table] = 1;
            }
            if ($tsize[$table] > $maxsize) {
                $maxsize = $tsize[$table];
                $result = $table;
            }
        }
        // Return largest table
        return $result;
    }