SQL SELECT DISTINCT和GROUP BY查询无效

Question

I have a tabel with e-mail adresses and additional data. Now i want to get all e-mailadresses that exsist multiple times in the table with different genders. I tried the folowing query:

SELECT email, COUNT(DISTINCT(gender)) FROM `email_data` WHERE COUNT(DISTINCT(gender)) > 1 GROUP BY email

I get the folowing result: #1111 - Invalid use of group function

I tried different variations including GROUP BY email, gender. but nothing seems to work. If i remove the WHERE part of the query it works. Can someone help me out?

Answer 1

You can't put aggregation functions in the WHERE clause. They go in the HAVING clause. However, it is usually more efficient to just compare the max and min values for this purpose:

SELECT email, COUNT(DISTINCT gender)
FROM `email_data`
GROUP BY email
HAVING MIN(gender) <> MAX(gender)