Why does "select count(*)" from nothing return 1

Question

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...

Answer 1

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