查找描述信息中包括robot的电影对应的分类名称以及电影数目,而且还需要该分类对应电影数量>=5部
CREATE TABLE IF NOT EXISTS film (
film_id smallint(5) NOT NULL DEFAULT '0',
title varchar(255) NOT NULL,
description text,
PRIMARY KEY (film_id));
CREATE TABLE category (
category_id tinyint(3) NOT NULL ,
name varchar(25) NOT NULL, `last_update` timestamp,
PRIMARY KEY ( category_id ));
CREATE TABLE film_category (
film_id smallint(5) NOT NULL,
category_id tinyint(3) NOT NULL, `last_update` timestamp);
解决思路
SELECT c.name, COUNT(fc.film_id) FROM
(select category_id, COUNT(film_id) AS category_num FROM
film_category GROUP BY category_id HAVING count(film_id)>=5) AS cc,
film AS f, film_category AS fc, category AS c
WHERE f.description LIKE '%robot%'
AND f.film_id = fc.film_id
AND c.category_id = fc.category_id
AND c.category_id=cc.category_id
找到对应电影数量>=5的所有分类,建立成虚表cc: (select category_id, count(film_id) as category_num from film_category group by category_id having count(film_id)>=5) as cc