为什么“选择计数(*)"?从无返回 1

使用 SQL Server 2012:

使用大师选择 *

收益

<块引用>

必须指定要从中选择的表

这正是我所期望的.

但有趣的是

使用大师选择计数(*)

返回 1.

有人可以向我解释一下这里计算的是什么吗?

并可能包括来源...

解决方案

SQL Server(在幕后)有效地将 from 应用于只有一行的虚拟表.因此，您的计数将得到 1.

选择测试"

会做同样的事情，例如，返回 'test' 一次.

就像 Oracle 中的 DUAL 表、DB2 中的 SYSDUMMY1 等.

根据要求，这里有几个关于此主题的 MS Connect 链接:

点击

更多点击

With SQL Server 2012 :

use master
select *

yields

Must specify table to select from

which is exactly what I would expect.

But the funny thing is that

use master
select count(*)

returns 1.

Can someone explain to me what is counted here?

Edit : And possibly include sources...

解决方案

SQL Server is (behind the curtain) effectively applying a from to a dummy table, which has only one row. Thus you will get 1 for your count.

select 'test'

will do the same thing, as an example, return 'test' one time.

It's like the DUAL table in Oracle, SYSDUMMY1 in DB2, etc.

As requested, here's a couple of links to MS Connect on this topic:

Clicky

More Clicky