我正在桌面上查询以下查询。
表：
+----+-------------+--------------+----------------------------+------------+--------+
| id | Qty_holding | Qty_reserved | created | tokenid_id | uid_id |
+----+-------------+--------------+----------------------------+------------+--------+
| 1 | 10 | 0 | 2018-01-18 10:52:14.957027 | 1 | 1 |
| 2 | 20 | 0 | 2018-01-18 11:20:08.205006 | 8 | 1 |
| 3 | 110 | 0 | 2018-01-18 11:20:21.496318 | 14 | 1 |
| 4 | 10 | 0 | 2018-01-23 14:26:49.124607 | 1 | 2 |
| 5 | 3 | 0 | 2018-01-23 15:00:26.876623 | 11 | 2 |
| 6 | 7 | 0 | 2018-01-23 15:08:41.887240 | 11 | 2 |
| 7 | 11 | 0 | 2018-01-23 15:22:48.424224 | 11 | 2 |
| 8 | 15 | 0 | 2018-01-23 15:24:03.419907 | 11 | 2 |
| 9 | 19 | 0 | 2018-01-23 15:24:26.531141 | 11 | 2 |
| 10 | 23 | 0 | 2018-01-23 15:27:11.549538 | 11 | 2 |
| 11 | 27 | 0 | 2018-01-23 15:27:24.162944 | 11 | 2 |
| 12 | 7.7909428 | 0.11459088 | 2018-01-23 15:27:24.168643 | 1 | 2 |
| 13 | 3 | 0 | 2018-01-23 15:36:51.412340 | 14 | 2 |
| 14 | 7.5585988 | 0.11459088 | 2018-01-23 15:36:51.417177 | 1 | 2 |
| 15 | 6 | 0 | 2018-01-24 08:43:46.635069 | 14 | 2 |
| 16 | 7.3262548 | 0.11459088 | 2018-01-24 08:43:46.639984 | 1 | 2 |
| 17 | 9 | 0 | 2018-01-24 10:09:08.207816 | 14 | 2 |
| 18 | 7.0939108 | 0.11459088 | 2018-01-24 10:09:08.212842 | 1 | 2 |
| 19 | 6 | 3 | 2018-01-24 13:43:08.929586 | 14 | 2 |
| 20 | 3 | 6 | 2018-01-24 14:49:56.960112 | 14 | 2 |
| 21 | 0 | 9 | 2018-01-24 14:50:33.423671 | 14 | 2 |
| 22 | 30 | 9 | 2018-01-24 14:51:14.865453 | 14 | 2 |
| 23 | 4.7704708 | 0.11459088 | 2018-01-24 14:51:14.870256 | 1 | 2 |
| 24 | 27 | 12 | 2018-01-24 14:56:56.914009 | 14 | 2 |
| 25 | 24 | 15 | 2018-01-24 14:57:56.475939 | 14 | 2 |
| 26 | 21 | 15 | 2018-01-24 14:58:06.750903 | 14 | 2 |
| 27 | 18 | 15 | 2018-01-24 15:02:43.203878 | 14 | 2 |
| 28 | 4.7705074 | 0.11459088 | 2018-01-24 15:02:43.224901 | 1 | 2 |
| 29 | 24 | 0 | 2018-01-24 15:03:40.421943 | 11 | 2 |
| 30 | 4.9535074 | 0.11459088 | 2018-01-24 15:03:40.441552 | 1 | 2 |
| 31 | 1 | 0 | 2018-01-26 10:35:33.173801 | 18 | 2 |
| 32 | 10 | 15 | 2018-01-26 12:46:03.780807 | 14 | 2 |
+----+-------------+--------------+----------------------------+------------+--------+
查询1：
select uid_id
, tokenid_id
, max(created) as max_created
from accounts_userholding
group
by uid_id
, tokenid_id
+--------+------------+----------------------------+
| uid_id | tokenid_id | max_created |
+--------+------------+----------------------------+
| 1 | 1 | 2018-01-18 10:52:14.957027 |
| 1 | 8 | 2018-01-18 11:20:08.205006 |
| 1 | 14 | 2018-01-18 11:20:21.496318 |
| 2 | 1 | 2018-01-24 15:03:40.441552 |
| 2 | 11 | 2018-01-24 15:03:40.421943 |
| 2 | 14 | 2018-01-26 12:46:03.780807 |
| 2 | 18 | 2018-01-26 10:35:33.173801 |
+--------+------------+----------------------------+
查询2：
select uid_id
, Qty_holding
, Qty_reserved tokenid_id
, max(created) as max_created
from accounts_userholding
group
by uid_id
, tokenid_id
+--------+-------------+--------------+------------+----------------------------+
| uid_id | Qty_holding | Qty_reserved | tokenid_id | max_created |
+--------+-------------+--------------+------------+----------------------------+
| 1 | 10 | 0 | 1 | 2018-01-18 10:52:14.957027 |
| 1 | 20 | 0 | 8 | 2018-01-18 11:20:08.205006 |
| 1 | 110 | 0 | 14 | 2018-01-18 11:20:21.496318 |
| 2 | 10 | 0 | 1 | 2018-01-24 15:03:40.441552 |
| 2 | 3 | 0 | 11 | 2018-01-24 15:03:40.421943 |
| 2 | 3 | 0 | 14 | 2018-01-26 12:46:03.780807 |
| 2 | 1 | 0 | 18 | 2018-01-26 10:35:33.173801 |
+--------+-------------+--------------+------------+----------------------------+
上面的Qty_holding值与最新日期不对应。例如，对于tokenid_id 14和uid_id，因为2最新记录是
| 32 | 10 | 15 | 2018-01-26 12:46:03.780807 | 14 | 2 |
但是上面的查询将qty_holding设为3。
有关mysql功能的任何见解都会有所帮助。谢谢！
答案 0 :(得分：1)
根据经验：在SELECT中将普通列与聚合函数混合使用时，需要使用GROUP BY。如果在SELECT中没有普通的列和聚合函数，请不要使用GROUP BY。
放入GROUP BY的东西全部来自SELECT但是聚合函数（和可能的常量）。
例如，如果您有查询：
select a, substring(b,3), 'x', max(y)
from yourtable
您需要使用GROUP BY。你省略'x'，因为它是一个常数，你省略了聚合函数。剩下的就转到了GROUP BY。
select a, substring(b,3), 'x', max(y)
from yourtable
group by a, substring(b,3)
以前的MySQL版本允许非常自由地使用GROUP BY，结果往往只是错误/不正确的代码。