Mysql error nested arithmetic in select

Question

When i am trying to execute this procedure it is showing an error.

USE `metro`;
DROP procedure IF EXISTS `transaction`;

DELIMITER $$
USE `metro`$$
CREATE DEFINER=`root`@`localhost` PROCEDURE `transaction`(
IN amount_p INT,
IN id_in INT,
IN id_out INT,
IN uidd INT
)
BEGIN

DECLARE uide INT;
DECLARE amt INT;
DECLARE NOW_AMT INT DEFAULT 0;

SELECT `amount` INTO amt FROM metro.wallet WHERE `uid`=uide;
INSERT INTO metro.transactions(`amount_deducted`,`time`,`station_id_in`,`station_id_out`,`uid`)
VALUES (amount_p,now(),id_in,id_out,uid);
SELECT uidd INTO uide;
SELECT uide;
SET NOW_AMT:=@amt+amount_p;

SELECT amt;
UPDATE metro.wallet SET `uid`=uide,`amount`=NOW_AMT;

END$$

DELIMITER ;

wallet is a table with uid and amount column.

Error code 1048, SQL state 23000: Column 'amount' cannot be null Line 1, column 1

Execution finished after 0 s, 1 error(s) occurred.

Execution :

call metro.transaction(112,1,1,1);

Answer 1

Perhaps wrap your AMOUNT in a case statement where you can return a default if it is NULL.

SELECT case when `amount` is NULL then '' else `amount` END as `amount` INTO amt FROM metro.wallet WHERE `uid`=uide;