为什么“select count（*）”从无返回1 [英] Why does "select count(*)" from nothing return 1

问题描述

使用SQL Server 2012：

 使用master 
 select * 
  
 
 
 
产生
 
 
 p> 
 
这正是我的期望。 
 
 
 
但有趣的是
 使用master 
 select count（*）
  
返回1. 
 
 
 
有人可以向我解释这里计算的是什么？
 
 
 
编辑：可能包括来源... 
解决方案
 SQL Server（幕后）有效地将一个from应用到一个只有一行的虚拟表。因此，你会得到1为你的计数。 
 选择'test'
  
会做同样的事情，例如，返回'test'一次。
 
 
 
它类似于Oracle中的DUAL表，DB2中的SYSDUMMY1 
 
 
 
根据需要，这里有一个指向MS Connect的链接：
 
 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

                        
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