将列设置为Null并在Postgresql中联接 [英] Setting Column to Null and Joining in Postgresql

问题描述

所以我有两个表。一个表包含两列。第二个表包含一列。但是，第二个表中的列与第一个表中第一列的列名称匹配：

So I have two tables. One table contains two columns. The second table contains one column. However the column in the second table matches the column name of the first column of the first table:

Table 1:
a       b
hello | 6
world | 7

Table 2:
a
new
t1

我想加入这两个表以得出：

I want to join these two tables to result in:

Table 3:
a         b
hello  | 6
world  | 7
new    | Null
t1     | Null

我研究了Cross Join和其他许多Join，但似乎都没有帮助

I have looked into Cross Join, and many other Joins but none of them seem to help in this case.

推荐答案

SELECT a, b FROM table_1
UNION ALL
SELECT a, NULL::INTEGER FROM table_b
;

对于某些其他数据库，不需要将上述类型转换为整数。

With some other databases, the cast to integer as above is not necessary.

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