$re = '/AS "(.+)\.(.+)"/m';
$str = ' table1.field1 AS "table1.field1",
table2.field2 AS "table2.field2",
table3.field3 AS "table3.field3",
table4.field1 AS "table4.field1",
table4.field1 AS "table5.field5",
table6.field6 AS "table6.field1",';
preg_match_all($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