Question

I am new to procedures and I am trying to implement them within my customer website.

I want to create a procedure to add a new customer. I want to check to make sure there phoneNumber is not already in the database. If it is, I want to display an error message. If the phone number is not in the db, I want to insert it into my CUSTOMER table.

I have implemented the following but I am getting an error. I am not sure if I am declaring variables right in MySQL, and I am not sure if the “if statement” is valid in the way I have done it. Also, how could I set the if statement query to a variable? If anyone could help, it would mean a lot. Thanks!

DELIMITER //
CREATE PROCEDURE add_Customer
(IN customerNum int, 
IN last varchar, 
IN first varchar)
BEGIN
DECLARE output var DEFAULT '';
IF SELECT CUSTOMER.customerNum FROM CUSTOMER WHERE CUSTOMER.customerNum= customerNum 
THEN
SET output= "Customer already exists!";
select output;
ELSE
INSERT INTO CUSTOMER VALUES (customerNum, last, first);
END IF;
END//
DELIMITER;

EDITED

DELIMITER //
CREATE PROCEDURE add_Customer
(IN customerNum int, 
IN last varchar, 
IN first varchar)
BEGIN
DECLARE output var DEFAULT '';
DECLARE var_num INT;
SELECT CUSTOMER.customerNum INTO var_num FROM CUSTOMER WHERE CUSTOMER.customerNum= customerNum 
if var_num IS NULL THEN
INSERT INTO CUSTOMER VALUES (customerNum, last, first);
ELSE
SET output= "Customer already exists!";
select output;
END IF;
END//
DELIMITER;

Answer 1

Try:

DECLARE var_num INT;
SELECT CUSTOMER.customerNum INTO var_num FROM CUSTOMER WHERE CUSTOMER.customerNum= customerNum
IF var_num IS NULL THEN
    INSERT INTO CUSTOMER VALUES (customerNum, last, first);
ELSE
    SET output= "Customer already exists!";
    select output;
ENDIF;
...