[英]SQL find number of columns
正確的查詢是這樣的:
SELECT m.title, COUNT(*)
FROM movies m JOIN
copies c
ON m.mid = c.mid
GROUP BY m.title
HAVING COUNT(*) > 2;
如果您不需要標題,那么甚至不需要JOIN
:
SELECT c.mid, COUNT(*)
FROM copies c
GROUP BY c.mid
HAVING COUNT(*) > 2;
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