排除count为零的MySQL结果行

Question

I have the following SQL query:

SELECT 
    COUNT(CASE WHEN u.account_new = 1 THEN u.user_id END) AS new_user, 
    COUNT(u.user_id) AS all_users, 
    c.country_name AS country 
FROM users u, countries c 
WHERE u.country_id = c.country_id 
GROUP BY u.country 

This shows a count of new users and total users grouped by country. I'd like to exclude rows where the count of new users is zero, but I'm not sure how to do this in the above SQL. At the moment I'm skipping them in PHP but thought there might be a better way to write the query.

Any suggestions are welcome.

Answer 1

Use this: (note the HAVING clause)

SELECT 
    COUNT(CASE WHEN u.account_new = 1 THEN u.user_id END) AS new_user, 
    COUNT(u.user_id) AS all_users, 
    c.country_name AS country 
FROM users u, countries c 
WHERE u.country_id = c.country_id 
GROUP BY u.country 
HAVING COUNT(CASE WHEN u.account_new = 1 THEN u.user_id END) > 0

Answer 2

This includes a better reading improvement for counting new users:

SELECT 
    SUM(u.account_new=1) AS new_user, 
    COUNT(u.user_id) AS all_users, 
    c.country_name AS country 
FROM users u, countries c 
WHERE u.country_id = c.country_id 
GROUP BY u.country 
HAVING SUM(u.account_new=1)>0