MySQLのTRIGGERとLAST_INSERT_IDについて

ddl.sql

USE last_insert_test;

CREATE TABLE table1 (
id1 int
) ENGINE=InnoDB;

CREATE TABLE table2 (
id2 int
) ENGINE=InnoDB;

INSERT INTO table2 VALUES(NULL); 

insert.sql

INSERT INTO table1 VALUES (NULL); 

last_insert_id.sql

SELECT LAST_INSERT_ID();

trigger.sql

delimiter //

CREATE TRIGGER table1_before_insert BEFORE INSERT ON table1 FOR EACH ROW
BEGIN
DECLARE last_id1 INT;
IF NEW.id1 IS NULL THEN
BEGIN
SELECT MAX(id1) INTO last_id1 FROM table1;
IF last_id1 IS NULL THEN
SET NEW.id1 = 101;
ELSE
SET NEW.id1 = last_id1 + 5;
END IF;
UPDATE table2 SET id2=LAST_INSERT_ID(NEW.id1);
END;
END IF;
END;//

delimiter ;