SQL以不同的条件多次选择同一列答案

【问题标题】：SQL select same column multiple times with different conditionsSQL以不同的条件多次选择同一列
【发布时间】：2019-06-26 03:59:25
【问题描述】：

我正在尝试显示几个分支机构及其对应的经理姓名、主管人数以及男性和女性员工的人数。但是，当我执行查询时会弹出以下错误消息，“列 'STAFF_T.stf_first_name' 在选择列表中无效，因为它不包含在聚合函数或 GROUP BY 子句中。”请帮帮我:)

SELECT  b.brc_id AS 'Branch ID',
        s.stf_first_name AS 'Manager First Name',
        s.stf_last_name AS 'Manager Last Name',
        (SELECT COUNT (sa.stf_position) FROM STAFF_T sa
         WHERE (sa.stf_position = 'Supervisor')) AS 'Number of Supervisor',
         (SELECT COUNT (sb.stf_position) FROM STAFF_T sb
          WHERE (sb.stf_position = 'Staff') AND
         (sb.stf_gender = 'Male')) AS 'Male Staff',
         (SELECT COUNT (sc.stf_position) FROM STAFF_T sc
          WHERE (sc.stf_position = 'Staff') AND
         (sc.stf_gender = 'Female')) AS 'Female Staff'
FROM BRANCH_T b, STAFF_T s
WHERE (b.brc_id = s.stf_brc_id) AND (b.brc_manager = s.stf_id)
GROUP BY b.brc_id

This is my current output 它目前显示主管、男性员工和女性员工的总数。它应该根据每个分支 id 显示主管和员工的数量。

【问题讨论】：

错误信息是不言自明的。该组的哪一行应该用于该值？分组时，如果未在GROUP BY 中列出，则该列只能与作用于整个组的聚合函数一起使用。
你能放一个预期输出的样本吗？
错误说明了一切，您需要在GROUP BY 子句中包含列 s.stf_first_name,s.stf_last_name
试过了，还是不行>_
@Unknown66 MJoy 给了你答案。如果您尝试过但仍然无效，请编辑您的问题以显示新代码。

标签： sql

【解决方案1】：

下面的查询应该可以工作，

SELECT 
    b.brc_id AS [Branch ID]
    ,s.stf_first_name AS [Manager First Name]
    ,s.stf_last_name AS [Manager Last Name]
    ,COUNT(CASE WHEN s.stf_position = 'Supervisor' THEN 1 ELSE 0 END) AS [Number of Supervisor]
    ,COUNT(CASE WHEN s.stf_position = 'Staff' AND s.stf_gender = 'Male' THEN 1 ELSE 0 END) AS [Male Staff]
    ,COUNT(CASE WHEN s.stf_position = 'Staff' AND s.stf_gender = 'Female' THEN 1 ELSE 0 END) AS [Female Staff]
FROM BRANCH_T b
INNER JOIN STAFF_T s 
    ON b.brc_id = s.stf_brc_id AND b.brc_manager = s.stf_id
GROUP BY b.brc_id,s.stf_first_name,s.stf_last_name

【讨论】：

【解决方案2】：

如错误消息所述，您正在混合聚合查询和非聚合查询。我会查询分支表并将其连接两次 - 一次在员工表上获取经理的详细信息，一次在员工表的聚合查询中获取计数：

SELECT b.brc_id AS 'Branch ID',
       m.stf_first_name AS 'Manager First Name',
       m.stf_last_name AS 'Manager Last Name',
       c.supervisor_count,
       c.male_staff,
       c.female_staff
FROM   branch_t b
JOIN   staff_t m ON b.brc_manager = m.stf_id
JOIN   (SELECT     stf_brc_id, 
                   COUNT(CASE sa.stf_position WHEN 'Supervisor' THEN 1 END)
                         AS supervisor_count,
                   COUNT(CASE WHEN sb.stf_position = 'Staff' AND
                                   sb.stf_gender = 'Male' THEN 1 END) AS male_staff, 
                   COUNT(CASE WHEN sb.stf_position = 'Staff' AND
                                   sb.stf_gender = 'Female' THEN 1 END) AS female_staff
        FROM     staff
        GROUP BY stf_brc_id) c ON c.stf_brc_id = b.brc_id

【讨论】：

【解决方案3】：

使用 RIGHT JOIN 可以使您的查询变得简单，如下所示-

SELECT  S.stf_brc_id,
MAX(CASE WHEN B.brc_id IS NULL THEN NULL ELSE S.stf_first_name END) F_name,
MAX(CASE WHEN B.brc_id IS NULL THEN NULL ELSE S.stf_last_name END) L_name,
SUM(CASE WHEN S.stf_position = 'Supervisor' THEN 1 ELSE 0 END ) 'Number of Supervisor',
SUM(CASE WHEN S.stf_position = 'Staff' AND S.stf_gender = 'Male' THEN 1 ELSE 0 END ) 'Male Staff',
SUM(CASE WHEN S.stf_position = 'Staff' AND S.stf_gender = 'Female' THEN 1 ELSE 0 END ) 'Female Staff'
FROM BRANCH_T B 
RIGHT JOIN STAFF_T S ON  B.brc_id = S.stf_brc_id AND B.brc_manager = S.stf_id
GROUP BY  S.stf_brc_id

【讨论】：