计算select查询返回的行数

Question

我需要计算以下查询返回的行数.

select m.Company_id
from Monitor as m
    inner join Monitor_Request as mr on mr.Company_ID=m.Company_id
    group by m.Company_id
    having COUNT(m.Monitor_id)>=5

我试过以下

select COUNT(*) from
(
select m.Company_id
from Monitor as m
    inner join Monitor_Request as mr on mr.Company_ID=m.Company_id
    group by m.Company_id
    having COUNT(m.Monitor_id)>=5)  

它在查询分析器中给出了一条错误消息,其中说明如下:

消息102,级别15,状态1,行7'''附近的语法不正确.

Answer 1

SQL Server需要您SELECT FROM或JOIN具有别名的子查询.

为子查询添加别名(在本例中x):

select COUNT(*) from
(
select m.Company_id
from Monitor as m
    inner join Monitor_Request as mr on mr.Company_ID=m.Company_id
    group by m.Company_id
    having COUNT(m.Monitor_id)>=5)  x

Answer 2

尝试将整个选择括在括号中,然后对其运行计数(*)

select count(*)
from
(
   select m.id
   from Monitor as m 
    inner join Monitor_Request as mr 
       on mr.Company_ID=m.Company_id   group by m.Company_id
    having COUNT(m.Monitor_id)>=5
) myNewTable

Answer 3

语法错误仅仅是由于子查询缺少别名:

select COUNT(*) from
(
select m.Company_id
from Monitor as m
    inner join Monitor_Request as mr on mr.Company_ID=m.Company_id
    group by m.Company_id
    having COUNT(m.Monitor_id)>=5)  mySubQuery  /* Alias */