Re: Duplicated values

[Bill Karwin]

There's no exception feature in triggers. The only thing you can do to force an error reliably is to define one of those columns as NOT NULL, and set the column to NULL if the "before" trigger finds a condition it doesn't like.

DELIMITER //
CREATE TRIGGER no_like_equal_numbers BEFORE INSERT ON Curses
FOR EACH ROW
BEGIN
IF NEW.column3 = NEW.column4 THEN
SET NEW.column3 = NULL;
END IF
END; //
DELIMITER ;

column3 should be defined NOT NULL, so the trigger above will cause the statement to fail if 1 = 1 as in your example.

Regards,
Bill K.