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 

我试图与以下

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) 

它给在查询分析器的错误消息，其表示如下：

消息102，级别15，状态1，行7不正确的语法靠近'）'。

Answer 1

SQL Server要求的子查询，你SELECT FROM或JOIN有一个别名。

一个别名添加到您的子查询（在这种情况下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

select COUNT(*) 
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 

Answer 3

尝试包裹整个选择括号，然后在该

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 4

语法运行COUNT（*）错误只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 */