按计数（*）mysql多个表分组答案

【问题标题】：group by count(*) mysql multiple tables按计数（*）mysql多个表分组
【发布时间】：2014-05-11 19:36:42
【问题描述】：

我试图对多个表进行计数（*），但将它们放在一个组中。

我在mysql中的查询是：

SELECT
  (SELECT COUNT(*) as 'Orders', Customer FROM table WHERE `date` = CURRENT_DATE()) as Client1, 
  (SELECT COUNT(*) as 'Orders', Customer FROM table2 WHERE `date` = CURRENT_DATE()) as Client2,
  (SELECT COUNT(*) as 'Orders', Customer FROM table3 WHERE `date` = CURRENT_DATE()) as Client3
  group by Customer

这就是我想要找回的：

+-------------+---------+---------+---------+
| Customer    | Client1 | Client2 | Client3 |
+-------------+---------+---------+---------+
| John Doe    | 88      | 19      | 0       |
+-------------+---------+---------+---------+
| Mary P      | 0       | 32      | 0       |
+-------------+---------+---------+---------+
| Scott K     | 11      | 25      | 31      |
+-------------+---------+---------+---------+

我唯一担心的是客户不会存在于其他表中，例如 - John Doe 只是 table1 中的客户 - 而不是 table2 或 table3。

与 Mary P 相同 - 她只是 table2 中的客户，而不是 table1 或 table 3 等。

【问题讨论】：

标签： mysql

【解决方案1】：

select a.Customer, sum(client1), sum(client2), sum(client3)
from
(
    select Customer, count(*) as client1, 0 as client2, 0 as client3 from table WHERE `date` = CURRENT_DATE() group by Customer
    union all
    select Customer, 0, count(*), 0 from table2 WHERE `date` = CURRENT_DATE() group by Customer
    union all
    select Customer, 0, 0, count(*) from table3 WHERE `date` = CURRENT_DATE() group by Customer
) as a
group by a.Customer

【讨论】：

【解决方案2】：

请在 union all 前使用() 喜欢

  select a.Customer, sum(client1), sum(client2), sum(client3)
    from
    (
        (select Customer, count(*) as client1, 0 as client2, 0 as client3 from table WHERE `date` = CURRENT_DATE() group by Customer)
        union all
        (select Customer, 0, count(*), 0 from table2 WHERE `date` = CURRENT_DATE() group by Customer)
        union all
        (select Customer, 0, 0, count(*) from table3 WHERE `date` = CURRENT_DATE() group by Customer)
    ) as a
    group by a.Customer

【讨论】：