如何将两个select语句组合成一个表，并使用两个独立的列？

Question

新到SQL，使用MS SQL Sever的管理工作室AdventureWorks示例数据库：

http://elsasoft.com/samples/sqlserver_adventureworks/sqlserver.spring.katmai.adventureworks/default.htm

试图在两个SELECT报表每个包含男女员工的COUNT结合起来。 我可以使用UNION ALL将两个计数返回到同一个表上的两行。

SELECT COUNT(HumanResources.Employee.Gender) AS 'Male Employees' 
FROM HumanResources.Employee 
WHERE Employee.Gender = 'M' 
UNION ALL 
SELECT COUNT(HumanResources.Employee.Gender) AS 'Female Employees' 
FROM HumanResources.Employee 
WHERE Employee.Gender = 'F'; 

但是我试图让每个M/F的COUNT在两个单独的列。管理得到两个单独的列出现，但计数不存在。

SELECT Set1.[Male Employees], Set2.[Female Employees] 
FROM 
( 
    SELECT COUNT(Employee.Gender) AS 'Male Employees' 
    FROM HumanResources.Employee 
    WHERE Employee.Gender = 'M' 
    ) as Set1 
INNER JOIN 
(
    SELECT COUNT(Employee.Gender) AS 'Female Employees' 
    FROM HumanResources.Employee 
    WHERE Employee.Gender = 'F' 
) as Set2 
on Set1.[Male Employees] = Set2.[Female Employees] 

我觉得我失去了一些东西明显..

Answer 1

您可以有条件聚集做到这一点：

SELECT SUM(CASE WHEN Employee.Gender = 'M' THEN 1 ELSE 0 END) AS 'Male Employees', 
     SUM(CASE WHEN Employee.Gender = 'F' THEN 1 ELSE 0 END) AS 'Female Employees' 
FROM HumanResources.Employee 

但你可以做到这一点野蛮，也直白道：

SELECT (SELECT COUNT(HumanResources.Employee.Gender) 
     FROM HumanResources.Employee 
     WHERE Employee.Gender = 'M') AS 'Male Employees', 
     (SELECT COUNT(HumanResources.Employee.Gender) 
     FROM HumanResources.Employee 
     WHERE Employee.Gender = 'F') AS 'Female Employees' 

第一种方法当然是优选的方式。