Question

我们说我有一张如下表：

id user_id   name   custom_field     status
1    123     lee     firstname         1
2    123     tan     lastname          1
3    123     chan     firstname        1
4    123     jackie   lastname         1
5    123     justin   firstname        0
6    123     wong     lastname         0
7    223     kevin    firstname        1
8    223     riley    lastname         1
9    223      john    firtname         1
10   223      poh     lastname         1

我想要做的是，foreach user_id我想确保只有1个firstname和1个lastname的状态1。（所以基本上我想通过id desc订购，并将那些不在前2名的人更新状态1到0）。我应该用什么sql脚本来完成这个？

Answer 1

您可以使用update查询执行此操作，例如：

update t join
       (select userid,
               max(case when custom_field = 'firstname' then id end) as maxid_first,
               max(case when custom_field = 'lastname' then id end) as maxid_last
        from t
        group by userid
       ) tt
       on tt.userid = t.userid and t.id not in (tt.maxid_first, tt.maxid_last)
    set status = 0;

编辑：

以上并不保证至少有一个“1”。为此：

update t join
       (select userid,
               max(case when custom_field = 'firstname' then id end) as maxid_first,
               max(case when custom_field = 'lastname' then id end) as maxid_last
        from t
        group by userid
       ) tt
       on tt.userid = t.userid
    set status = (t.id in (tt.maxid_first, tt.maxid_last));

MySQL更新特定列

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