MS SQL变量在同一语句中从count添加值

Question

我有这个Select语句

select Id, UserName, from UserTable where Department= @DepartmentInput

和一个变量来计算部门用户的数量

@UserCounter

如果语句在while循环中运行，是否可以通过select语句将count（来自部门的用户数）添加到@UserCounter中？

Answer 1

假设sql-server：

select Id, UserName, @UserCounter = Count(*) OVER (Partition By Department)
from UserTable 
where Department= @DepartmentInput

否则一个简单的子查询也应该起作用：

select Id, UserName, @UserCounter = (select count(*) from UserTable
                                     where Department= @DepartmentInput)
from UserTable 
where Department= @DepartmentInput

数据库应该足够聪明以优化该查询，以便不需要为每个（匹配）行设置子查询。