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