Question

我想展示每个部门的文员和经理人数。

这是我的代码：

SELECT DISTINCT 
    deptno AS 'DEPARTMENT NUMBER',
    (SELECT COUNT(*) 
     FROM EMP
     WHERE JOB = 'CLERK'
     GROUP BY DEPTNO) AS 'NUMBER OF CLERKS',
    (SELECT COUNT(*) 
     FROM EMP
     WHERE JOB = 'MANAGER'
     GROUP BY DEPTNO) AS 'NUMBER OF MANAGER'
FROM 
    EMP
GROUP BY 
    deptno

以下是返回的错误：

子查询返回的值超过1。当子查询遵循=，！=，＆lt;，＆lt; =，＆gt;，＆gt; =或子查询用作表达式时，不允许这样做。

我想像这样显示结果：

+-------------------+------------------+---------------------+
| DEPARTMENT NUMBER | NUMBER OF CLERKS | NUUMBER OF MANAGERS |
+-------------------+------------------+---------------------+
| 10                | 1                |    1                |
| 20                | 2                |    1                |
| 30                | 1                |    1                |
+-------------------+------------------+---------------------+

Answer 1

这种计算通常最容易使用sum + case进行此类计算：

SELECT
    deptno,
    sum (case when JOB = 'CLERK' then 1 else 0 end) AS [NUMBER OF CLERKS],
    sum (case when JOB = 'MANAGER' then 1 else 0 end) AS [NUMBER OF MANAGERS]
FROM 
    EMP
GROUP BY 
    deptno

Answer 2

您也可以使用PIVOT

执行此操作

    DECLARE @EMP table (Dep_No INT, Job VARCHAR(20))
    INSERT INTO @EMP
    VALUES (10,'clerk'),
           (10,'clerk'),
           (10,'clerk'),
           (10,'Manager'),
           (20,'clerk'),
           (20,'clerk'),
           (20,'clerk'),
           (20,'clerk'),
           (20,'clerk'),
           (20,'clerk'),
           (20,'Manager'),
           (20,'Manager'),
           (30,'clerk'),
           (20,'Manager'),
           (30,'clerk')

    SELECT Dep_No , [clerk] Number_Of_Clerks ,[Manager] Number_of_Managers 
     FROM @EMP
        PIVOT
            (
            COUNT(Job) FOR Job in ([clerk], [Manager])
            ) W

使用SELECT子句下的子查询显示多个行和列

2 个答案: