This article brings you relevant knowledge about MySQL. It mainly introduces what a recommendation algorithm is, what problems this algorithm can help us solve, and how to use MySQL to implement a simple recommendation algorithm. Interested Let's take a look at it together, friends. I hope it will be helpful to everyone.
Using MySQL to implement a simple recommendation algorithm
The recommendation algorithm is a technology that is often encountered. Basically the problem solved is: if you like book A, then you'll probably like book B.
In this article, we use MySQL and disassemble and implement a simple recommendation algorithm based on data statistics.
First, create a data table of books that the user likes, which represents user_id likes book_id.
CREATE TABLE user_likes ( user_id INT NOT NULL, book_id VARCHAR(10) NOT NULL, PRIMARY KEY (user_id,book_id), UNIQUE KEY book_id (book_id, user_id) ); CREATE TABLE user_likes_similar ( user_id INT NOT NULL, liked_user_id INT NOT NULL, rank INT NOT NULL, KEY book_id (user_id, liked_user_id) );
Insert 4 pieces of test data
INSERT INTO user_likes VALUES (1, 'A'), (1, 'B'), (1, 'C'); INSERT INTO user_likes VALUES (2, 'A'), (2, 'B'), (2, 'C'), (2,'D'); INSERT INTO user_likes VALUES (3, 'X'), (3, 'Y'), (3, 'C'), (3,'Z'); INSERT INTO user_likes VALUES (4, 'W'), (4, 'Q'), (4, 'C'), (4,'Z');
means: user 1 likes A, B, C, user 2 likes A, B, C, D, user 3 likes X, Y ,C,Z, user 4 likes W,Q,C,Z.
Taking user 1 as an example to calculate recommended books, we need to calculate the similarity between user 1 and other users, and then sort according to the similarity.
Clear the similarity data table
DELETE FROM user_likes_similar WHERE user_id = 1;
Calculate the user similarity data table
INSERT INTO user_likes_similar SELECT 1 AS user_id, similar.user_id AS liked_user_id, COUNT(*) AS rank FROM user_likes target JOIN user_likes similar ON target.book_id= similar.book_id AND target.user_id != similar.user_id WHERE target.user_id = 1 GROUP BY similar.user_id ;
You can see that the found similarity result is
user_id, liked_user_id, rank 1, 2, 2 1, 3, 1 1, 4, 1
and then based on Sort by similarity, and take the top 10 books, which are the recommended books.
SELECT similar.book_id, SUM(user_likes_similar.rank) AS total_rank FROM user_likes_similar JOIN user_likes similar ON user_likes_similar.liked_user_id = similar.user_id LEFT JOIN user_likes target ON target.user_id = 1 AND target.book_id = similar.book_id WHERE user_likes_similar.user_id = 1 AND target.book_id IS NULL GROUP BY similar.book_id ORDER BY total_rank desc LIMIT 10;
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