Database Trigger for Basic

okay, the first i will explain about database trigger.

Database trigger is procedural code that is automatically executed in response to certain events on a particular table or view in a database. The trigger is mostly used for keeping the integrity of the information on the database. For example, when a new record (representing a new worker) is added to the employees table, new records should be created also in the tables of the taxes, vacations, and salaries.

A trigger is defined to activate when an INSERT, DELETE, or UPDATE statement executes for the associated table. A trigger can be set to activate either before or after the triggering statement. For example, you can have a trigger activate before each row that is inserted into a table or after each row that is updated.

let'sstart with the following example:

create database mytrigger;

create table test (
code varchar(5) not null,name varchar(35) not null,
primary key (code))

create table test2(
code varchar(5) not null,namevarchar(35) not null,
primary key (code))

create table tran (
code varchar(5) not null,
trancode varchar(5),summary double,
primary key ncode(code,trancode))

delimiter $$
 
create trigger auto_insert_test2
before insert on test for each row
begin
insert into test2 (code,name) values (NEW.code,NEW.name);
end$$
 
create trigger auto_update_test2
before update on test for each row
begin
update test2 set name=NEW.name where code=NEW.code;
end$$
 
create trigger auto_delete_test2
before delete on test for each row
begin
delete from test2 where code=OLD.code;
delete from tran where code=OLD.code;
end$$