TSQL ORDER BY 首先或最后一个空值(在底部或顶部) [英] TSQL ORDER BY with nulls first or last (at bottom or top)

问题描述

我有一个日期列，其中包含一些 NULL.我想按日期列 ASC 排序，但我需要 NULL 位于底部.如何在 TSQL 上做到这一点?

I have a date column which has some NULL. I want to order by the date column ASC, but I need the NULL s to be at the bottom. How to do it on TSQL?

推荐答案

在标准 SQL 中，您可以指定放置空值的位置:

In standard SQL you can specify where to put nulls:

order by col asc nulls first
order by col asc nulls last
order by col desc nulls first
order by col desc nulls last

但是 T-SQL 不符合这里的标准.NULL 的顺序取决于你在 T-SQL 中是升序还是降序:

but T-SQL doesn't comply with the standard here. The order of NULLs depends on whether you sort ascending or descending in T-SQL:

order by col asc -- implies nulls first
order by col desc -- implies nulls last

对于整数，您可以简单地按负数排序:

With integers you could simply sort by the negatives:

order by -col asc -- sorts by +col desc, implies nulls first
order by -col desc -- sorts by +col asc, implies nulls last

但这对于日期(或与此相关的字符串)是不可能的，因此您必须首先按 is null/is not null 排序，然后再按您的列排序:

But this is not possible with dates (or strings for that matter), so you must first sort by is null / is not null and only then by your column:

order by case when col is null then 1 else 2 end, col asc|desc -- i.e. nulls first
order by case when col is null then 2 else 1 end, col asc|desc -- i.e. nulls last

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