“分组”自动保证“order by”？ [英] Does "group by" automatically guarantee "order by"?

问题描述

group by子句是否自动保证结果将按该键排序？换句话说，它是否足够写：

Does "group by" clause automatically guarantee that the results will be ordered by that key? In other words, is it enough to write:

select * 
from table
group by a, b, c

或者必须写

select * 
from table
group by a, b, c
order by a, b, c

我知道eg在MySQL我不必，但我想知道如果我可以依靠它跨越SQL实现。是否保证？

I know e.g. in MySQL I don't have to, but I would like to know if I can rely on it accross the SQL implementations. Is it guaranteed?

推荐答案

group by 。 DB被设计为尽可能快地获取数据，并且仅在必要时进行排序。

group by does not order the data neccessarily. A DB is designed to grab the data as fast as possible and only sort if necessary.

如果您需要有保证的订单，请添加订单。

So add the order by if you need a guaranteed order.

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