Question

请不要咬我这个，但我是mysql的新手，我在WHERE子句中使用假名有些问题。我认为可以在select语句中定义的聚合函数使用假名。这是我的查询

SELECT a.name, s.name, COUNT(e.id) as total FROM athletes a 
INNER JOIN sports s on s.id = a.sport_id 
INNER JOIN events e on s.id = e.sport_id 
WHERE total >=2 GROUP BY a.name

但是，我收到错误“WHERE子句中的未知列总数”。谁能告诉我这样做是否正确？

Answer 1

您不能在where子句中使用别名。您需要在having

中使用它

SELECT 
a.name, 
s.name, 
COUNT(e.id) as total FROM athletes a 
INNER JOIN sports s on s.id = a.sport_id 
INNER JOIN events e on s.id = e.sport_id  
GROUP BY a.name having total >=2

Answer 2

而不是WHERE total＆gt; = 2你可以使用HAVING（总＆gt; = 2）

HAVING：

SELECT a.name, s.name, COUNT(e.id) as total 
FROM athletes a 
INNER JOIN sports s on s.id = a.sport_id 
INNER JOIN events e on s.id = e.sport_id  
GROUP BY a.name, s.name 
HAVING (total >= 2 );

Answer 3

Yo不能在where子句中使用列别名。你必须在where clasue中使用表达式COUNT(e.id)，或者你可以在having子句中使用别名：

SELECT a.name, s.name, COUNT(e.id) as total FROM athletes a INNER JOIN sports s on s.id = a.sport_id INNER JOIN events e on s.id = e.sport_id WHERE COUNT(e.id)>=2 GROUP BY a.name

或

SELECT a.name, s.name, COUNT(e.id) as total FROM athletes a INNER JOIN sports s on s.id = a.sport_id INNER JOIN events e on s.id = e.sport_id having total>=2 GROUP BY a.name

在MYSQL查询中使用WHERE子句中的假名

3 个答案: