The statement which allows you to execute a set of SQL ststements on the basis of certain conditions is known as MYSQL IF statement.

Below I am explaining the structure for if-else statement.

MySQL IF statement syntax-

 IF expression THEN 
       statements;
    END IF;

MySQL IF-ELSE statement syntax-

IF expression THEN
   statements;
ELSE
   else-statements;
END IF;

MySQL IF-ELSE-IF statement syntax-

IF expression THEN
   statements;
ELSEIF expression THEN
   statements;
...
ELSE
   statements;
END IF;

MySQL IF example

In following example we describe, how to use the IF ESLEIF ELSE statement. The GetCustomerLevel() stored procedure accepts two parameters customer number and customer level.

First, it gets the credit limit from the customers table.

Then, based on the credit limit, it determines the customer level: PLATINUM , GOLD , and SILVER .

The parameter p_customerlevel stores the level of the customer and is used by the calling program.

DELIMITER $$ 

    CREATE PROCEDURE GetCustomerLevel(
        in  p_customerNumber int(11), 
        out p_customerLevel  varchar(10))
    BEGIN
        DECLARE creditlim double;

        SELECT creditlimit INTO creditlim
        FROM customers
        WHERE customerNumber = p_customerNumber;

        IF creditlim > 50000 THEN
     SET p_customerLevel = 'PLATINUM';
        ELSEIF (creditlim <= 50000 AND creditlim >= 10000) THEN
            SET p_customerLevel = 'GOLD';
        ELSEIF creditlim < 10000 THEN
            SET p_customerLevel = 'SILVER';
        END IF;

    END$$