$re = '/(?i)(?<=[^\w])[-+]?[\d\.]+(e[-+]?\d+)?/';
$str = 'SELECT pop1990, pop2000, 500, -50,-0.5, -5E-100, 4e+20, 3e10
FROM foo
WHERE pop1990 IN (5, 100, 7.8,25;)';
preg_match_all($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