mysql group_concat

$insertSql = " select max(case when goodtest.boxID = @idbox then  @title := CONCAT_WS(',',@title,goodtest.isotope)";
    $insertSql .= " else @title := goodtest.isotope end  ) as isotope,  ";   
    $insertSql .= "  @idbox:=goodtest.boxID as boxID  ";   
    $insertSql .= " from goodtest group by goodtest.boxID  ";       
    $query ="SELECT @title = NULL, @idbox = 0; ";   
    $query .= "INSERT INTO test(isotope, boxID)  ";


very very bad mysql!