将 2 个 SQL SELECT 结果集合并为一个 [英] Joining 2 SQL SELECT result sets into one

问题描述

我有 2 个选择语句，返回的数据如下:

I've got 2 select statements, returning data like this:

Select 1
col_a   col_b

Select 2
col_a   col_c

如果我做联合，我会得到类似的东西

If I do union, I get something like

col_a col_b

并且行加入.我需要的是这样:

And rows joined. What i need is getting it like this:

col_a  col_b  col_c

加入 col_a

推荐答案

使用 JOIN 连接子查询并使用 ON 表示每个子查询中的行必须匹配的位置:

Use JOIN to join the subqueries and use ON to say where the rows from each subquery must match:

SELECT T1.col_a, T1.col_b, T2.col_c
FROM (SELECT col_a, col_b, ...etc...) AS T1
JOIN (SELECT col_a, col_c, ...etc...) AS T2
ON T1.col_a = T2.col_a

如果 col_a 的某些值在 T1 中但不在 T2 中，则可以使用 LEFT OUTER JOIN 代替.

If there are some values of col_a that are in T1 but not in T2, you can use a LEFT OUTER JOIN instead.

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