Question

I have make a procedure where two queries return values for

a and b

Substract of a and b is c

c = a-b;

if value of c is positive then procedure return correct value and if value of c is in negative then procedure return NULL.

This is my procedure.

DELIMITER $$

USE `db`$$

DROP PROCEDURE IF EXISTS `getOutStandingBalance`$$

CREATE DEFINER=`root`@`%` PROCEDURE `getOutStandingBalance`(OUT Total DOUBLE SIGNED,IN OID INT)
    DETERMINISTIC
    COMMENT 'A procedure'
BEGIN
    DECLARE Credit DOUBLE;
    DECLARE Debit  DOUBLE;
    SELECT SUM(transaction.Amount) INTO Credit FROM `transaction` WHERE transaction.IsDeleted=0 AND transaction.IsCredit=1 AND transaction.OID=OID;

    SELECT SUM(transaction.Amount) INTO Debit FROM `transaction` WHERE transaction.IsDeleted=0 AND transaction.IsCredit=0 AND transaction.OID=OID;

    SET Total = (Credit-Debit);
END$$

DELIMITER ;

Answer 1

If no rows are found for either of the credit or debit for the transaction, the variables will be NULL. In SQL, any calculation with a NULL results in a NULL.

To fix, do this:

SET Total = ifnull(Credit, 0) - ifnull(Debit, 0);

Also, change the signature to

OUT Total decimal(16,2)

or similar. Why are you using DOUBLE SIGNED?