Searches all the columns names in a SQL query, works on wide range of fields including calculated fields

getColumnsFromQuery.php

<?php

/**
 * <p>Searches all the columns names in the given query, backticks are ignored</p>
 * <p>Works on wide range of fields:</p>
 * - column
 * - column alias
 * - column AS alias
 * - table.column
 * - table.column alias
 * - table.column AS alias
 * <p>including calculated fields e.g.:</p>
 * - COUNT(table.column) alias
 * - EXISTS (SELECT column FROM table.column2 SEPARATOR ';') alias
 * - GROUP_CONCAT(table.column ORDER BY table.column2 SEPARATOR ';') alias
 * 
 * @author   Pedro Sanção <pedro@sancao.com.br>
 * @license  GNU General Public License version 2
 * @param string $sql well formed SQL query
 */
function searchColumns($sql) {
	$fromPos = 0;
	$limit = substr_count($sql, 'FROM');
	for ($i = 0; $i < $limit; $i++) {
		$fromPos = strpos($sql, 'FROM', $fromPos + 1);
		if(substr_count($sql, '(', 0, $fromPos) === substr_count($sql, ')', 0, $fromPos)) {
			$sql = trim(substr($sql, 0, $fromPos));
			break;
		}
	}
	$matches = array();
	preg_match_all('/(?<=^SELECT |, |\) )([a-z]+\.)?([a-z]+ )?(as )?([a-z]+)(?= ?,|$)/im', $sql, $matches);
	return array_pop($matches);
}