在MYSQL查询的WHERE子句中使用化名

Question

Please don't bite me for this, but I'm new to mysql and I have some problem with using pseudonym in WHERE clause. I thought that it is possible to use pseudonym for aggregate function, defined in the select statement. Here is my query

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 

But, I catch an error "Unknown column total in WHERE clause". Could anyone tell me if it is right to do query like this?

Answer 1

You can not use alias in the where clause. You need to use that in 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 having total >=2

Answer 2

Instead of WHERE total >=2 you can use HAVING (total >= 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 can not use an column alias in where clause. you have to use the expression COUNT(e.id) in where clasue or you can use the alias in a having clause:

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 

or

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