An empty output from a Mysql stored procedure

Question

I created the following simple procedure for my database class assignment

DROP PROCEDURE IF EXISTS cs431_movie_database.must_watch_movies;
DELIMITER //
CREATE PROCEDURE cs431_movie_database.must_watch_movies()
BEGIN
    -- variables that stores the fetch data for each row
    DECLARE movie_name VARCHAR(50);
    DECLARE distributor VARCHAR(20);
    DECLARE release_year INT;
    
    -- for exception handling
    DECLARE row_not_found TINYINT DEFAULT FALSE;
    
    -- the final output string
    DECLARE output VARCHAR(400) DEFAULT '';
    
    -- a cursor that goes throw each row of the movies database
    DECLARE movies_cursor CURSOR FOR
        SELECT title, Distributor, YEAR(release_date) AS release_year
        FROM cs431_movie_database.movies
        WHERE gross > 2
        ORDER BY title ASC;
        
    -- handler when there is no more row found by the cursor
    DECLARE CONTINUE HANDLER FOR NOT FOUND 
        SET row_not_found = TRUE;
        
    OPEN movies_cursor;
    -- put fetch data into procedure variables then concat them into the output string
    WHILE row_not_found = FALSE DO
        FETCH movies_cursor INTO movie_name, distributor, release_year;
        SET output = CONCAT(output, '\'', movie_name, '\', \'',distributor, '\', \'', release_year, '\'| ');
    END WHILE;
    
    CLOSE movies_cursor;
    -- gets the output
    SELECT output;
    
END //
DELIMITER ;

Where my expected output when I call it would be something like

'movie name 1', 'distributor 1', 'release year for movie 1' | 'movie name 2', 'distributor 2', 'release year for movie 2' | 'movie name 3', ....

But instead, I got a null string came back to me, I'm not sure what went wrong with my code, please help

Answer 1

Like @Barmar offers in a comment:

SELECT GROUP_CONCAT(CONCAT('\'', 
                           movie_name,  
                           '\', \'', 
                           distributor,  
                           '\', \'',  
                           YEAR(release_date),  
                           '\'')  
                     ORDER BY title ASC 
                     SEPARATOR '| ')
FROM cs431_movie_database.movies
WHERE gross > 2;