protected function getIndexSqlDefinition($indexName, $indexSpec)
    {
        if ($indexSpec['type'] == 'using') {
            return sprintf('index "%s" using (%s)', $indexName, $this->implodeColumnList($indexSpec['columns']));
        } else {
            return sprintf('%s "%s" (%s)', $indexSpec['type'], $indexName, $this->implodeColumnList($indexSpec['columns']));
        }
    }