在PostgreSQL中添加两个关系的列 [英] Adding columns of two relations in postgresql

问题描述

我有两个关系，例如Relation1和Relation2。关系1的列为A，B，C，关系2的列为D，E，F。

I have two relations such as relation1 and relation2. relation1 has columns of A,B,C and relation2 has columns of D,E,F.

我想将关系1的A与关系2的D相加，其中C = F对于在lation2中不存在的C值必须出现而在relation1中不出现的F值也必须出现。

I want to add A of relation1 with D of relation2 where C = F. For the C values which do not exist in relation2 must appear and F values which do not appear in relation1 also must appear How to do this postgresql?

推荐答案

使用 FULL [OUTER] JOIN 可以包含任一侧的行，而另一侧不包含匹配行：

Use a FULL [OUTER] JOIN to include rows from either side without a matching row on the other side:

SELECT COALESCE(r1.a, 0) + COALESCE(r2.d, 0) AS a_d
FROM   relation1      r1
FULL   JOIN relation2 r2 ON r1.c = r2.f

也可以使用 COALESCE（） 即可 NULL 值替换缺少的列。

Also use COALESCE() to catch NULL values substituted for missing columns.

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