books ratings, MySQL

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DROP TABLE IF EXISTS ratings;
DROP TABLE IF EXISTS books;

CREATE TABLE IF NOT EXISTS ratings
    (`User_ID` int, `ISBN` varchar(20), `Book_Rating` int)
;
    
INSERT INTO ratings
    (`User_ID`, `ISBN`, `Book_Rating`)
VALUES
    (244662, 0373630689, 3),
    (19378, 0812515595, 2),
    (238625, 0441892604, 5),
    (180315, 0140439072, 1),
    (242471, 3548248950, 1)
;

CREATE TABLE IF NOT EXISTS books
    (`ISBN` varchar(20), `Book_Title` varchar(11), `Book_Author` varchar(10), `Year_Of_Publication` int, `Publisher` varchar(10))
;
    
INSERT INTO books
    (`ISBN`, `Book_Title`, `Book_Author`, `Year_Of_Publication`, `Publisher`)
VALUES
    (0393000753, 'A Reckoning', 'May Sarton', 1981, 'W W Norton'),
    (0812515595, 'A Reckoning', 'May Sarton', 1981, 'W W Norton'),
    (0441892604, 'A Reckoning', 'May Sarton', 1981, 'W W Norton'),
    (0140439072, 'A Reckoning', 'May Sarton', 1981, 'W W Norton'),
    (3548248950, 'A Reckoning', 'May Sarton', 1981, 'W W Norton')
;

SET @sql = NULL;

SELECT Concat(
         'SELECT ISBN, ',
         Group_Concat( x SEPARATOR ','),
         ' FROM ratings GROUP BY ISBN '
       )
INTO @sql
FROM (
  SELECT Concat('Max( CASE WHEN User_ID = ', User_ID, ' THEN Book_Rating END ) As User_', User_ID ) As x
  FROM ratings 
  GROUP BY User_ID
  ORDER BY User_ID
) x;

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;


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