public function getSupportedCollations()
    {
        if ($this->supportedCollations === null) {
            $supportedCollations = [];
            $rs = $this->executeQuery('SHOW COLLATION');
            while (($row = $rs->fetch(PDO::FETCH_ASSOC)) !== false) {
                if (!isset($row['Collation']) || !isset($row['Charset'])) {
                    throw new Exception(t('Unrecognized result of the "%s" database query.', 'SHOW COLLATION'));
                }
                $supportedCollations[strtolower($row['Collation'])] = strtolower($row['Charset']);
            }
            $this->supportedCollations = $supportedCollations;
        }

        return $this->supportedCollations;
    }