PostgreSQL中的DISTINCT WHERE查询 [英] DISTINCT WHERE query in PostgreSQL

问题描述

我正在尝试在postgresql中的一个选择的不同查询中放置where子句，但是没有运气。

I'm trying to put a where clause in a select distinct query in postgresql but having no luck.

我想执行以下操作：

select distinct on (state_or_county) state_or_county 
from locations 
where country = "USA"

我已经在mysql中做过很多次了，不明白为什么它不起作用。

I've done this many times in mysql and can't understand why this isn't working.

有人可以更正查询吗？还是解释一下为什么它不起作用？

Can someone please correct the query? Or explain just why it isn't working?

推荐答案

在PostgreSQL中，字符串文字必须用单引号引起来：

In postgresql a string literal must be wrapped in single quotes:

select distinct on (state_or_county) state_or_county 
from locations 
where country = 'USA'

如有必要，双引号用于标识符：

Double quotes are used for identifiers, if needed:

select distinct on ("state_or_county") "state_or_county" 
from "locations" 
where "country" = 'USA'

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