eZ\Publish\Core\Persistence\Doctrine\DoctrineExpression::subString PHP Method

Note: Not SQL92, but common functionality.

public subString ( string $value, integer $from, integer $len = null ) : string
$value	string	the target $value the string or the string column.
$from	integer	extract from this characeter.
$len	integer	extract this amount of characters.
return	string	sql that extracts part of a string.

    public function subString($value, $from, $len = null)
    {
        return $this->platform->getSubstringExpression($value, $from, $len);
    }

DoctrineExpression