Question

我有一张表可以跟踪学生的不同资格。资格定期更新，因此许多学生拥有相同资格的多个记录。

我试图仅返回每个学生的每个资格的最新记录，没有重复。

到目前为止，我有这个，但我仍然坚持要删除重复的type_scrn并返回最新的记录。

SELECT scrn.*
FROM cert_scrn scrn
WHERE scrn.id_scrn = (SELECT scrn2.id_scrn 
    FROM cert_scrn scrn2
    WHERE scrn.id_scrn = scrn2.id_scrn
    AND ( scrn2.type_scrn = 1
        OR scrn2.type_scrn = 11
        OR scrn2.type_scrn = 12
        OR scrn2.type_scrn = 13 )
    ORDER BY scrn2.expiredate_scrn DESC  LIMIT 1) 
ORDER BY  scrn.idstu_scrn

返回：

id_scrn | idstu_scrn | type_scrn | expiredate_scrn
-------------------------------------------------
15      | 58         | 1         | 2010-01-26
1539    | 58         | 1         | 2015-06-21
5790    | 58         | 11        | 2016-02-20
5791    | 58         | 12        | 2016-02-20
5792    | 58         | 13        | 2016-02-20

我需要回复：

id_scrn | idstu_scrn | type_scrn | expiredate_scrn
---------------------------------------------------
1539    | 58         | 1         | 2015-06-21
5790    | 58         | 11        | 2016-02-20
5791    | 58         | 12        | 2016-02-20
5792    | 58         | 13        | 2016-02-20

Answer 1

您需要加入子查询，查找每个idstu_scn，type_scrn组的最长日期。

因此，获取max(date)的查询将是：

select idstu_scrn, type_scrn, max(expiredate_scrn) mdate
  from cert_scrn
  group by idstu_scrn, type_scrn

然后我们再次需要再次加入cert_scrn表，找到其余的详细信息。

select scrn.*
  from cert_scrn scrn
    inner join (
      select idstu_scrn, type_scrn, max(expiredate_scrn) mdate
        from cert_scrn
        group by idstu_scrn, type_scrn ) q
      on scrn.idstu_scrn = q.idstu_scrn and scrn.type_scrn = q.type_scrn and scrn.expiredate_scrn = q.mdate
  where scrn.type_scrn = 1
    or scrn.type_scrn = 11
    or scrn.type_scrn = 12
    or scrn.type_scrn = 13

demo fiddle here

Answer 2

请根据主键检查这个，在这种情况下似乎正常工作：

SELECT * FROM cert_scrn WHERE id_scrn IN 
(SELECT MAX(id_scrn) FROM cert_scrn GROUP BY idstu_scrn, type_scrn);

为每个用户返回唯一的记录行

2 个答案: