最佳答案
正确的查询是这样的:
SELECT m.title, COUNT(*)
FROM movies m JOIN
copies c
ON m.mid = c.mid
GROUP BY m.title
HAVING COUNT(*) > 2;
如果您不需要标题,则甚至不需要 JOIN
:
SELECT c.mid, COUNT(*)
FROM copies c
GROUP BY c.mid
HAVING COUNT(*) > 2;
关于mysql - SQL查找列数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/44101723/