UNION ALL 是否保证结果集的顺序 [英] Does UNION ALL guarantee the order of the result set

问题描述

我可以确定以下脚本的结果集总是像这样 O-R-D-E-R 排序吗?

Can I be sure that the result set of the following script will always be sorted like this O-R-D-E-R ?

SELECT 'O'
UNION ALL
SELECT 'R'
UNION ALL
SELECT 'D'
UNION ALL
SELECT 'E'
UNION ALL
SELECT 'R'

能否证明有时顺序不同?

Can it be proved to sometimes be in a different order?

推荐答案

没有固有的顺序，必须使用ORDER BY.对于您的示例，您可以通过将 SortOrder 添加到每个 SELECT 来轻松完成此操作.这将按照您想要的顺序保存记录:

There is no inherent order, you have to use ORDER BY. For your example you can easily do this by adding a SortOrder to each SELECT. This will then keep the records in the order you want:

SELECT 'O', 1 SortOrder
UNION ALL
SELECT 'R', 2
UNION ALL
SELECT 'D', 3
UNION ALL
SELECT 'E', 4
UNION ALL
SELECT 'R', 5
ORDER BY SortOrder

除非您在查询中特别提供订单，否则您无法保证订单.

You cannot guarantee the order unless you specifically provide an order by with the query.

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