How do I CONCAT() a string with itself using a curser in mysql

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SQL

my table is like this: SPJ table(snumber, pnumber, jnumber, qty)

my string varchar outputs null when I concat it to itself.

what I want is parenthesized the pairs of ( supplier-number, total-qty-supplied) for all supplier who supply parts.

this is what I have:

DELIMITER $$
    CREATE DEFINER=`root`@`localhost` PROCEDURE `supplierInfo`(OUT `string` VARCHAR(300))
    BEGIN
    DECLARE s VARCHAR(40);
    DECLARE number VARCHAR(4);
    DECLARE qty  int(6);
    DECLARE FOUND BOOLEAN DEFAULT TRUE;

    DECLARE cur CURSOR FOR
    SELECT DISTINCT spj.snumber, SUM(spj.qty)
    FROM spj
    GROUP BY spj.snumber;
    DECLARE CONTINUE HANDLER FOR NOT FOUND
    SET FOUND = false;
    OPEN cur; 
    FETCH cur INTO number, qty;
    WHILE(FOUND)DO
    SET string = CONCAT(string,'(',number,' ',qty,')');
    FETCH cur INTO number, qty;
    END WHILE;
    CLOSE cur;
    END$$
    DELIMITER ;

What I have tried:

SET string = CONCAT(string,'(',number,' ',qty,')');