$re = '/^select\s+(?<columns>.*?)\s+from\s+(.*?)?((where\s+(?<where>.*?))?(order by\s+(?<order>.*?))?(limit\s+(?<limit>(.*?)))?);/i';
$str = 'select * from mytable where x=10 and t="abc" order by abc, def LIMIT 10,10;';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php