Doctrine\DBAL\Platforms\PostgreSqlPlatform::getSubstringExpression PHP Method

    public function getSubstringExpression($value, $from, $length = null)
    {
        if ($length === null) {
            return 'SUBSTRING(' . $value . ' FROM ' . $from . ')';
        }
        return 'SUBSTRING(' . $value . ' FROM ' . $from . ' FOR ' . $length . ')';
    }