MySQL Trigger syntax for ordering based on user id - mysql

Question

I would like to create a trigger on the FRIENDS table so that friend pairs are ordered and there aren't duplicate entries with the same friends. The following trigger is throwing a syntax error at BEGIN IF (:new.USER1_ID > :new.USER2_ID) ... -- how is this trigger supposed to be formatted?
CREATE TABLE USERS (
USER_ID INTEGER NOT NULL,
FIRST_NAME VARCHAR(100) NOT NULL,
LAST_NAME VARCHAR(100) NOT NULL,
YEAR_OF_BIRTH INTEGER,
MONTH_OF_BIRTH INTEGER,
DAY_OF_BIRTH INTEGER,
SSN INTEGER,
EMAIL VARCHAR(100),
PHONE INTEGER,
PWD VARCHAR(100),
ADDRESS VARCHAR(500),
PRIMARY KEY(USER_ID)
);
CREATE TABLE FRIENDS (
USER1_ID INTEGER,
USER2_ID INTEGER,
FOREIGN KEY (USER1_ID) REFERENCES USERS(USER_ID) ON DELETE CASCADE,
FOREIGN KEY (USER2_ID) REFERENCES USERS(USER_ID) ON DELETE CASCADE,
PRIMARY KEY(USER1_ID, USER2_ID),
CHECK(USER1_ID!=USER2_ID)
);
CREATE TRIGGER FRIENDS_TRIGGER
BEFORE INSERT ON FRIENDS FOR EACH ROW
BEGIN
DECLARE TEMP INTEGER
BEGIN
IF (:new.USER1_ID > :new.USER2_ID) THEN
SET TEMP = :new.USER1_ID
SET :new.USER1_ID = :new.USER2_ID
SET :new.USER2_ID = TEMP
END IF
END
/

Answer 1

There are several problems. You need to terminate statements with semicolons, and so you also need to change the delimiter so the entire create trigger is treated as a single statement. :new should also be NEW. And you have an extra BEGIN thrown in there.
DELIMITER //
CREATE TRIGGER FRIENDS_TRIGGER
BEFORE INSERT ON FRIENDS
FOR EACH ROW
BEGIN
DECLARE TEMP INTEGER;
IF (NEW.USER1_ID > NEW.USER2_ID) THEN
SET TEMP = NEW.USER1_ID;
SET NEW.USER1_ID = NEW.USER2_ID;
SET NEW.USER2_ID = TEMP;
END IF;
END; //
DELIMITER ;