MySQL: SELECT and COUNT in same query

问题

I have these two tables:

CITY TABLE

CLUB TABLE

What I'm trying to do, is to select with the same query all cities that contain published clubs (published field set to 1) and the total of clubs published in that city.

At the moment, I am doing it with two steps, but I would like to improve performance by merging these in just one query.

SELECT c.id, c.name, c.slug 
FROM city c, club cl 
WHERE c.id = cl.city_id 
AND ( SELECT COUNT(*) 
      FROM club cl, city c 
      WHERE cl.city_id = c.id AND cl.published = 1) > 0
GROUP BY c.id

After this, I'm doing a query for each city just to get the COUNT.

回答1:

Something like this:-

SELECT city.id, city.name, city.slug, COUNT(club.id) AS club_count
FROM city
INNER JOIN club
ON city.id = club.city_id
WHERE club.published = 1
GROUP BY city.id, city.name, city.slug
HAVING club_count > 0

来源：https://stackoverflow.com/questions/13511664/mysql-select-and-count-in-same-query