MySQL trigger simple usage example

CREATE TRIGGER name,time,event ON table_name FOR EACH ROW trigger_stmt

CREATE TABLE test1(a1 INT);
CREATE TABLE test2(a2 INT);
CREATE TABLE test3(a3 INT NOT NULL AUTO_INCREMENT PRIMARY KEY);
CREATE TABLE test4(
  a4 INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
  b4 INT DEFAULT 0
);
DELIMITER //
CREATE TRIGGER testref BEFORE INSERT ON test1
  FOR EACH ROW BEGIN
    INSERT INTO test2 SET a2 = NEW.a1;
  DELETE FROM test3 where a3 = NEW.a1;
    UPDATE test4 SET b4 = b4 + 1 WHERE a4 = NEW.a1;
  END
  //
DELIMITER ;
INSERT INTO test3(a3) VALUES (NULL), (NULL), (NULL), (NULL), (NULL), (NULL), (NULL), (NULL), (NULL), (NULL), (NULL), (NULL);
INSERT INTO test4(a4) VALUES (0), (0), (0), (0), (0), (0), (0), (0), (0), (0), (0);
//Start testing INSERT INTO test1 VALUES (1), (3), (1), (7), (1), (8), (4), (4);

SHOW TRIGGERS \G; //View all SELECT * FROM information_schema.TRIGGERS where TRIGGER_NAME = 'testref';

DROP TRIGGER testref;

CREATE TABLE persons (name VARCHAR(40), num int);

CREATE TABLE sales (name VARCHAR(40), sum int);

CREATE TRIGGER num_sum AFTER INSERT ON persons
FOR EACH ROW INSERT INTO sales VALUES (NEW.name,7*NEW.num);

INSERT INTO persons VALUES ('xiaoxiao',20),('xiaohua',69);
SELECT * FROM persons;
SELECT *FROM sales;