为什么 HAVING col > AVG(col) 不返回任何行？

Question

此视图显示每个劫匪、他们入狱的年数、实施的抢劫次数和他们的总收入（21 行）。

然后我尝试创建另一个视图以进一步操作上面视图中的数据。我希望我的新视图仅显示 NoYears（入狱服刑）= 0 且 NoRobberies 大于平均抢劫次数的劫匪的昵称。

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

然而，当我尝试 SELECT * FROM ActiveRobbers3 时，returns 没有行。谁能看到我的问题？干杯

Answer 1

也许这行得通：

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

Answer 2

你的问题含糊不清。 table 的所有数据或与特定 "Nickname" 有关的数据的平均值 NoRobberies。

案例 1：NoRobberies 所有数据的平均值

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

案例 2：相应昵称 NoRobberies 的平均值 "Nickname"

CREATE VIEW ActiveRobbers3
AS
SELECT Nickname,NoRobberies

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

注意：仅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

为什么 HAVING col > AVG(col) 不返回任何行？

Why is HAVING col > AVG(col) returning no rows?

sql

postgresql

psql