php，mysql_query(）语句，提示内存溢出

<code> $check_status = 2;    $art_act_reslut = mysql_query(    "SELECT * FROM (    SELECT     publish_time,    article_id as id,    user_id as user_brand_id,    article_text as text,     article_thumbs as thumds_person_num,    sort_weight,    '' as title,    article_comment_number as article_comment_number FROM article     WHERE recommend = '$recommend' and check_status = '$check_status' and publish_time > '$timestamp'    UNION    SELECT     publish_time,    activity_id as id,    brand_id as user_beand_id,    activity_content as text,    join_persons as thumds_person_num,    sort_weight,    activity_title as title,    '' as article_comment_number FROM activity    WHERE recommend = '$recommend' and check_status = '$check_status' and publish_time > '$timestamp') stain     ORDER BY stain.publish_time DESC, stain.sort_weight DESC");    unset($recommend);    unset($check_status);    //赋值到cards    for($i=0;$i<20;$i++) {        $cards_arr = array();        $art_act_reslut_value =  mysql_fetch_assoc($art_act_reslut);            //给相应的参数赋值        $id = $art_act_reslut_value["id"];        $user_brand_id = $art_act_reslut_value["user_brand_id"];        $text = $art_act_reslut_value["text"];        $thumds_person_num = $art_act_reslut_value["thumds_person_num"];        $article_comment_nummber = $art_act_reslut_value["article_comment_number"];        $publish_time = $art_act_reslut_value["publish_time"];        $title = $art_act_reslut_value["title"];        $sort_weight = $art_act_reslut_value["sort_weight"];        unset($art_act_reslut_value);</code>