CREATE TABLE t1 ( a INT, b INT );
CREATE TABLE t2 ( a INT, b INT );
CREATE TABLE t3 ( a INT AUTO_INCREMENT KEY, b INT );

INSERT INTO t1 (a) VALUES (1);

delimiter //;
CREATE TRIGGER tr1
BEFORE INSERT ON t3
FOR EACH ROW 
BEGIN 
  UPDATE a_nonextisting_table SET a = 1;
END//

CREATE TRIGGER tr2
AFTER INSERT ON t2
FOR EACH ROW
BEGIN 
  INSERT INTO t3 ( b ) VALUES ( 1 );
END//
delimiter ;//

--disable_abort_on_error
CREATE TABLE IF NOT EXISTS t3 ( a INT, b INT )
SELECT a, b FROM t1;
--enable_abort_on_error

CREATE TABLE t2 ( a INT, b INT )
SELECT a, b FROM t1;