php - 如何在 mysql/php 中向我的插入查询添加序号。不是 auto_increment

Question

我想在每次用户创建考试时插入一个连续的项目编号。 每次他创建考试时，它都会重新启动到 1。我非常需要你们的帮助，各位。更多的权力。 :)

这是我的代码:

$examid = $_SESSION['examid'];
$itemnum = 1;

$sql = mysql_query("INSERT INTO exam_questions (question_description, question_type, question_exam_id) VALUES ('$question', '$type', '$examid')")or die(mysql_error());
$lastinsertid = mysql_insert_id();
mysql_query("UPDATE exam_questions SET question_set_id='<??????????>' WHERE question_id='$lastinsertid' LIMIT 1")or die(mysql_error());

Answer 1

尝试通过连接来实现:

UPDATE exam_questions eq cross join
       (select max(question_set_id) as qsi
        from exam_questions
        where question_id='$lastinsertid'
       ) as const
    SET eq.question_set_id = const.qsi + 1
    WHERE question_id='$lastinsertid';