本文介绍了如何串联Postgres SELECT中的列?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我在表foo中有两个字符串列a和b.
I have two string columns a and b in a table foo.
select a, b from foo返回值a和b.但是，a和b的串联不起作用.我试过了:
select a, b from foo returns values a and b. However, concatenation of a and b does not work. I tried :
select a || b from foo
和
select a||', '||b from foo
根据评论更新:两列均为character(2)类型.
Update from comments: both columns are type character(2).
推荐答案
问题出在值中为null.则串联不能与null一起使用.解决方法如下:
The problem was in nulls in the values; then the concatenation does not work with nulls. The solution is as follows:
SELECT coalesce(a, '') || coalesce(b, '') FROM foo;
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