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MySQL:max()和groupby的问题-值错误

greatest-n-per-group mysql

Tim · 技术社区 · 16 年前

我对SQL语句有问题:

select a.id as ID, a.dur as DUR, DATE(FROM_UNIXTIME(timestampCol)) as date, 
 a_au.re as RE, a_au.stat as STAT from b_c
  inner join c on b_c.c_id = c.id
  inner join a on c.id = a.c_id
  inner join a_au on a.id = a_au.id
  inner join revi on a_au.rev = revi.rev
  where b_c.b_id = 5

我得到这个结果:

ID  DUR         date   RE  STAT
-------------------------------
31, 10, '2010-07-14', 2200, 0
31, 10, '2010-07-14', 2205, 0
31, 10, '2010-07-14', 2206, 2
31, 10, '2010-07-14', 2207, 0
31, 10, '2010-07-14', 2210, 2
31, 10, '2010-07-15', 2211, 0
31, 10, '2010-07-14', 2213, 1
32, 10, '2010-07-14', 2203, 0
32, 10, '2010-07-14', 2204, 0
32, 10, '2010-07-14', 2208, 2
32, 10, '2010-07-14', 2209, 0
32, 10, '2010-07-15', 2212, 2

现在我想得到一个ID和日期组合的结果行。我还想得到这个结果行的最高雷诺数。

select a.id as ID, a.dur as DUR, DATE(FROM_UNIXTIME(timestampCol)) as date, 
 max(a_au.re) as RE, a_au.stat as STAT from b_c
  inner join c on b_c.c_id = c.id
  inner join a on c.id = a.c_id
  inner join a_au on a.id = a_au.id
  inner join revi on a_au.rev = revi.rev
  where b_c.b_id = 5
  group by ID, date

现在我得到这个结果:

ID  DUR         date   RE  STAT
-------------------------------
31, 10, '2010-07-14', 2213, 0
31, 10, '2010-07-15', 2211, 0
32, 10, '2010-07-14', 2209, 0
32, 10, '2010-07-15', 2212, 2

一切似乎都很好,我每天有一个结果行/ID组合和行与最高的重新编号。但是:列STAT没有正确的值!

31, 10, '2010-07-14', 2213, 0

必须具有状态1:

31, 10, '2010-07-14', 2213, 1

所以我的陈述肯定有错。似乎MySQL使用它找到的第一个STAT列值。但是我想要一个对应的。

我在这里看到了其他的话题: Selecting all corresponding fields using MAX and GROUP BY 但是我不能把它转移到我的SQL语句中。

提前多谢&致以最诚挚的问候。

1 回复 | 直到 9 年前

OMG Ponies 16 年前

用途:

SELECT a.id as ID, 
       a.dur as DUR, 
       DATE(FROM_UNIXTIME(timestampCol)) as date, 
       a_au.re as RE, 
       a_au.stat as STAT 
 FROM b_c
 JOIN c on b_c.c_id = c.id
 JOIN a on c.id = a.c_id
 JOIN a_au on a.id = a_au.id
 JOIN revi on a_au.rev = revi.rev
 JOIN ( SELECT a.id as ID, 
               DATE(FROM_UNIXTIME(timestampCol)) as date, 
               MAX(a_au.re) as Max_RE
          FROM b_c
          JOIN c on b_c.c_id = c.id
          JOIN a on c.id = a.c_id
          JOIN a_au on a.id = a_au.id
          JOIN revi on a_au.rev = revi.rev
         WHERE b_c.b_id = 5 
      GROUP BY a.id, DATE(FROM_UNIXTIME(timestampCol))) x ON x.id = a.id
                                                         AND x.date = DATE(FROM_UNIXTIME(timestampCol))
                                                         AND x.max_re = a_au.re
WHERE b_c.b_id = 5