MySql 5.7 ORDER BY子句不在GROUP BY子句中,并且包含非聚合列

Question

我试图找出而不在my.ini中禁用"only_full_group_by"

这是我的查询:

SELECT 
  p.title,
  COUNT(t.qty) AS total 
FROM
  payments t 
  LEFT JOIN products AS p 
    ON p.id = t.item 
WHERE t.user = 1 
GROUP BY t.item
ORDER BY t.created DESC;

和表格:

支付方式:

id     item   user   created
============================
1      1      1      2017-01-10
2      2      1      2017-01-11
3      3      1      2017-01-12
4      4      1      2017-01-13
5      1      1      2017-01-14

产品介绍:

id     title    created
==========================
1      First     2016-12-10
1      Second    2016-12-11
1      Third     2016-12-12
1      Fourth    2016-12-13

最后的结果看起来应该是谎言:

Name    Total
First   2
Second  1
Third   1
Fourth  1

但是,如果我将查询更改为GROUP BY t.item, t.created错误消失了,但我最终得到的是五条记录而不是四条记录,这不是我想要的.由于我是根据"item"字段对项目进行分组,因此应该只有四个记录

Answer 1

这是您的查询:

SELECT p.title, COUNT(t.qty) AS total 
-------^
FROM payments t LEFT JOIN
     products AS p 
     ON p.id = t.item 
WHERE t.user = 1 
GROUP BY t.item
---------^
ORDER BY t.created DESC;
---------^

指向的地方有问题.请注意,SELECT并且GROUP BY指的是不同的列.在a中LEFT JOIN,你(几乎)总是希望通过第一个表中的某些内容进行聚合,而不是第二个表中的内容.

这ORDER BY是另一个问题.您没有按此列聚合,因此您需要确定所需的值.我猜MIN()或MAX():

SELECT p.title, COUNT(t.qty) AS total 
FROM payments t LEFT JOIN
     products AS p 
     ON p.id = t.item 
WHERE t.user = 1 
GROUP BY p.title
ORDER BY MAX(t.created) DESC;

我还要补充一点,这COUNT(t.qty)是可疑的.通常qty是指"数量",你想要的是总和: SUM(t.qty).