2.9 KiB
CREATE PROCEDURE RateModel ( IN cid VARCHAR ( 20 ), IN m VARCHAR ( 20 ), IN r INT ) BEGIN-- 1. 插入新评分记录 INSERT INTO ratings ( customer_id, model, rating_time, rating ) VALUES ( cid, m, NOW( ), r ) -- 2. 更新 Products 表的总评分和评分次数 INSERT IGNORE INTO Products ( total_rating, number_of_ratings ) VALUES ( 0, 0 );-- 3. 计算该型号的最新总评分和评分次数 UPDATE products SET total_rating = ( SELECT COALESCE( SUM( rating ), 0 ) FROM Ratings WHERE model = m ), number_of_ratings = ( SELECT COUNT( * ) FROM Ratings WHERE model = m ) WHERE model = m;
END -- -- 2 CREATE PROCEDURE DeleteRating ( IN cid ( 10 ), IN m ( 10 ), ) BEGIN CALL RateModel ( p_customer_id, p_model, NULL );
END -- 3
CREATE PROCEDURE CleanRatings ( INT cid ( 10 ) INT m ( 10 ) ) BEGIN
DELETE
FROM
Rating
WHERE
customer_id = cid
AND model = m
AND rating_time < (
SELECT
max_time
FROM
( SELECT MAX( r2.rating_time ) AS max_time FROM Ratings AS r2 WHERE r2.customer_id = p_customer_id AND r2.model = p_model ) AS t
);
END;
CALL RateModel ( '1122334455', '1001', 3 );
CALL RateModel ( '1122334455', '1001', 2 );
CALL RateModel ( '9999999999', '1001', 5 );
CALL RateModel ( '1122334455', '1001', NULL );
CALL RateModel ( '9999999999', '1001', 4 );
CALL RateModel ( '9999999999', '1001', NULL );
CALL RateModel ( '1122334455', '1001', 2 );
CALL CleanRatings ( '9999999999', '1001' ); CALL CleanRatings ( '1122334455', '1001' );
-- 3 CREATE VIEW AverageRatings(model, average_rating) AS SELECT model, COALESCE(SUM(rating) / COUNT(), 0) AS average_rating FROM Ratings GROUP BY model HAVING COUNT() > 0; -- 仅包含至少有1次评分的型号
-- 3.b DELIMITER // CREATE FUNCTION BestModel() RETURNS VARCHAR(20) DETERMINISTIC BEGIN DECLARE max_avg FLOAT; DECLARE best_model VARCHAR(20);
-- 步骤1：获取最高平均评分
SELECT MAX(average_rating) INTO max_avg FROM AverageRatings;
-- 步骤2：若无评分，返回NULL
IF max_avg IS NULL THEN
RETURN NULL;
END IF;
-- 步骤3：获取平均评分最高的所有型号，选择最新非空评分的型号
SELECT model INTO best_model
FROM (
-- 子查询：获取平均评分最高的型号，及其最新非空评分时间
SELECT
ar.model,
MAX(CASE WHEN r.rating IS NOT NULL THEN r.rating_time ELSE NULL END) AS latest_non_null_time
FROM AverageRatings ar
JOIN Ratings r ON ar.model = r.model
WHERE ar.average_rating = max_avg
GROUP BY ar.model
ORDER BY latest_non_null_time DESC -- 按最新非空评分时间降序
LIMIT 1 -- 取最新的一个
) AS temp;
RETURN best_model;
END // DELIMITER ;
-- 3.c