Question

我有两个单独的SELECT语句，它们分别是GROUP-BY，例如：

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

我非常希望将这两个SELECT连接在一起以组合它们的列，例如：

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，因为MySQL在抱怨

您的SQL语法有错误; 检查对应的手册您的MySQL服务器版本正确的语法在'LEFT JOIN附近使用选择 x为x2

如果可以的话，对我的语法有什么问题的想法？

非常感谢！

Answer 1

这有效

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)
);

可替换地，

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

两者都会导致

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

Answer 2

有几种方法可以实现这一目标：

最佳：在分组之前加入表格如下：

SELECT a.x, y, z, n, o
  FROM a INNER JOIN b ON a.x = b.x
 GROUP BY a.x, b.x;

从两个查询中选择子查询，如下所示：

SELECT *
FROM       (SELECT x, y, z FROM a GROUP BY x) AS a
INNER JOIN (SELECT x, n, o FROM b GROUP BY x) AS b
        ON a.x = b.x;

Answer 3

您也可以使用此查询：
SELECT a.x, a.y, a.z, b.x, b.o, b.n FROM a, (SELECT x, n, o FROM b GROUP BY x) as b WHERE a.x = b.x GROUP BY a.x;

MySQL：是否可以将GROUP-BY的结果加入两个SELECT？

3 个答案: