添加数量时如何在存储过程中不显示减值

I want display selected table with quantity adding using stored procedure in php

here is my code

DELIMITER $$ CREATE DEFINER=`root`@`localhost` PROCEDURE `GetCustomerLevel`(IN p_barcode INT, OUT q_value INT) BEGIN   
DECLARE q1 int;   DECLARE q2 int;   
DECLARE q3 int;   DECLARE total int;   
SET total :=0;   
SELECT coalesce(sum(adjustment_quantity), 0) INTO q1 FROM adjustment_inventory WHERE item_barcode = p_barcode;   SELECT coalesce(sum(opening_stock), 0) INTO q2 FROM openingstock WHERE item_barcode = p_barcode;   SELECT coalesce(sum(inwardquantity), 0) INTO q3 FROM inwardmaster WHERE item_barcode = p_barcode; set total = q1+q2+q3; set q_value = total; 
END$$ DELIMITER ;

When i call the particular data display but i want display selected table and if adding quantity display only positive and 0 not minus value show in php