php无限递归查询子id子类根据父分类父ID查询所有子分类子ID

function posterity($fid)
 {
  global $connection;
 //static $children=array();
 global $children;
 $sql = "SELECT DEPT_ID  FROM department WHERE DEPT_PARENT= $fid";
     $cursor = exequery( $connection, $sql);
     while ($row = mysql_fetch_array($cursor)) {




     $children[]=$row[DEPT_ID];
     $pid    = $row[DEPT_ID]; 

       posterity($pid);


 }return $children;
 }