为什么没有“ SELECT foo。* ... GROUP BY foo.id”？在Postgres？

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我有这样的查询：

select foo.*, count(bar.id) from foo inner join bar on foo.id = bar.foo_id group by foo.id

这对于SQLite和MySQL很好用。但是，Postgres抱怨我没有在 group by 子句中包括foo的所有列。为什么是这样？

This worked great with SQLite and MySQL. Postgres however, complains about me not including all columns of foo in the group by clause. Why is this? Isn't it enough that foo.id is unique?

推荐答案

以防其他人迷失了这个问题：

Just in case other people stumble over this question:

从PostgreSQL 9.1开始，在group by子句中列出主键的列就足够了（因此问题中的示例现在可以使用）。

Starting with PostgreSQL 9.1 it's sufficient to list the columns of the primary key in the group by clause (so the example from the question would work now).