为什么HAVING col＆gt; AVG（col）没有返回任何行？

Question

这是一个显示每个强盗，他们的监禁年数，所犯抢劫的数量和他们的总收入（21行）的视图。

然后我尝试创建另一个视图以进一步操纵上面视图中的数据。我希望我的新视图只显示劫匪的绰号，其NoYears（在监狱服刑）= 0且其NoRobberies大于平均抢劫数。

CREATE VIEW ActiveRobbers3
AS
SELECT Nickname
FROM ActiveRobbers2
WHERE NoYears = 0
GROUP BY Nickname, NoRobberies
HAVING NoRobberies > AVG(NoRobberies);

但是当我尝试SELECT * FROM ActiveRobbers3时，这不会返回任何行。谁能看到我的问题？干杯

Answer 1

你的问题很模糊。表中所有数据的平均NoRobberies或与特定“昵称”相关的数据。

案例1：所有数据中NoRobberies的平均值

CREATE VIEW ActiveRobbers3
AS
SELECT Nickname
FROM ActiveRobbers2
WHERE NoYears = 0
AND NoRobberies > (select AVG(NoRobberies) from ActiveRobbers2);

案例2：各个昵称“昵称”的平均值NoRobberies

CREATE VIEW ActiveRobbers3
AS
SELECT Nickname,NoRobberies

FROM ActiveRobbers2
WHERE NoYears = 0
GROUP BY Nickname
Having NoRobberies > AVG(NoRobberies);

注意：只有当昵称至少有两行具有不同的NoRobberies时，case-2才会提供数据。示例代码适用于MySQL

Answer 2

也许这有效：

CREATE VIEW ActiveRobbers3
AS
SELECT Nickname
FROM ActiveRobbers2, 
(SELECT AVG(AVG_NoRobberies) as AVG_NoRobberies FROM ActiveRobbers2) as b
WHERE NoYears = 0
AND NoRobberies > b.AVG_NoRobberies