Question

我有两个表用户，订单

每个表的下面一列

users(table)
id

orders(table)
user_id

我如何获得订单数量为1,2,3,4 .... n的用户数量？

喜欢吗？

users count    |   order count
999            |   1
100            |   2
 80            |   3
 70            |   4
 60            |   5
 50            |   6

到目前为止，我一直在尝试

SELECT cnt.uid as u_cnt, cnt.ocnt as or_cnt
FROM (
  SELECT u.id as uid, COUNT(o.id) as o_cnt
  FROM users as u
  INNER JOIN orders o on u.id = o.user_id
) as cnt;
GROUP BY or_cnt

但是我只得到1个u_cnt并求和or_cnt

Answer 1

此处需要两个级别的group by子句：首先，您需要按用户分组并计算每个用户所拥有的订单数。然后，您需要获取该结果，将订单数量分组并计算有多少用户拥有该订单数量。

最简单的方法可能是使用子查询，其中内部查询和外部查询都有一个group by子句：

SELECT cnt.ocnt as or_cnt, COUNT(*) as user_count
FROM (
  SELECT u.id as uid, COUNT(o.id) as o_cnt
  FROM users as u
  INNER JOIN orders o on u.id = o.user_id
  GROUP BY u.id -- This was missing in your original query
) as cnt
GROUP BY or_cnt

Answer 2

您可以使用两个级别的聚合。更重要的是，您不需要JOIN。您需要的所有信息都在orders中：

SELECT o_cnt, COUNT(*) as user_count
FROM (SELECT o.user_id, COUNT(*) as o_cnt
      FROM orders o
      GROUP BY o.user_id 
     ) u
GROUP BY o_cnt
ORDER BY o_cnt;

MySQL如何对GROUP BY计数列？

2 个答案: