MySQL:是否可以将GROUP-BY的结果加入两个SELECT中? [英] MySQL: Is it possible to JOIN the GROUP-BY'd results to two SELECTs?

问题描述

我有两个单独的SELECT语句，它们分别是GROUP-BY的，例如:

I have two separate SELECT statements which are both GROUP-BY'd separately e.g.:

SELECT x, y, z FROM a GROUP BY x
SELECT x, n, o FROM b GROUP BY x

我非常想将这两个SELECT结合在一起以合并其列，例如:

I would very much like to JOIN these two SELECTs together to combine their columns, such as:

SELECT x as x1, y, z FROM a GROUP BY x 
LEFT JOIN (
  SELECT x as x2, n, o FROM b GROUP BY x)
ON x1=x2;

这可能吗?我问是因为MySQL抱怨

Is this possible? I ask because MySQL is complaining

您的SQL语法有错误； 检查对应的手册 您的MySQL服务器版本 在'LEFT JOIN附近使用正确的语法 选择 x作为x2

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'LEFT JOIN SELECT x as x2

如果可能的话，我对我的语法有什么疑问吗?

If this is possible, any thoughts on what's wrong with my syntax?

非常感谢！

推荐答案

有效

select * from (
    (select 1 a,2 b,3 c) t1 left join (select null a,2 b,5 c) t2 on (t1.b=t2.b)
);

或者，

select * from (
    (select 1 a,2 b,3 c) t1 left join (select null a,2 b,5 c) t2 using (b)
);

两者都导致

+---+---+---+------+---+---+
| a | b | c | a    | b | c |
+---+---+---+------+---+---+
| 1 | 2 | 3 | NULL | 2 | 5 |
+---+---+---+------+---+---+
1 row in set (0.00 sec)

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