mysql - 根据最新创建时间选择唯一行

Question

这是我的查询:

SELECT br.employee_id AS rat_id,
       br.rating_comment,
       br.created_at,
       br.id
FROM employee_followers
LEFT JOIN employee_ratings AS br ON employee_followers. employee_id = br.employee_id
WHERE employee_followers.employee_id IN
    (SELECT `employee_id`
     FROM employee_followers
     WHERE user_id =32)
GROUP BY br.id
ORDER BY created_at DESC

我得到了什么:

rat_id    rating_comment        created_at              id
18        superb developer      2016-02-19 18:26:54     82
9         james to manoj-joshi  2016-02-19 16:42:17     84
50        james to prem         2016-02-19 13:05:30     83
50        pinal to prem         2016-02-19 12:20:00     73
50        prem to premal-joshi  2016-02-19 11:40:52     78
18        prem to mukund        2016-02-19 11:21:52     77
18        pinal to mukund       2016-02-18 11:37:00     76
9         mukund rate to mitesh 2016-02-15 22:34:14     51
9         Not a bad.            2016-02-10 00:16:31     45
9         sda                   2016-02-08 01:36:33     39

我想要什么:

rat_id    rating_comment        created_at              id
18        superb developer      2016-02-19 18:26:54     82
9         james to manoj-joshi  2016-02-19 16:42:17     84
50        james to prem         2016-02-19 13:05:30     83

Answer 1

试试这个

SELECT rat_id,rating_comment, MAX(created_at) AS created, id FROM (
SELECT br.employee_id AS rat_id,
       br.rating_comment,
       br.created_at,
       br.id
FROM employee_followers
LEFT JOIN employee_ratings AS br ON employee_followers. employee_id = br.employee_id
WHERE employee_followers.employee_id IN
    (SELECT `employee_id`
     FROM employee_followers
     WHERE user_id =32)
GROUP BY br.id
ORDER BY created_at DESC) AS temp GROUP BY temp.rat_id