Triggers of MySQL

trigger
1. Create a trigger
#rType: insert update delete
#Format
#CREATE TRIGGER trigger name trigger time trigger event
#      on  表  from each now
# SQL statement




#Add a message to display the prompt message
delimiter $$
CREATE TRIGGER ct_student AFTER INSERT
     on student for each ROW
              set @info = 'Added successfully';
$$
delimiter;




insert into student
   values('160504118','Liu Yiming','Male','1998-05-18','Han','Communist Youth League member');


delimiter $$
   CREATE TRIGGER ct_update AFTER UPDATE
      on student for each ROW
      BEGIN
       set @inf='Cannot be changed';
      end $$
delimiter;




#Create a trigger that does not allow users to modify records in the table
begin WORK;
  update student
     set nation='Mongolian'
          where student ID = '160504118';
rollback work;
select @ inf;
select * from student;
    where student ID = '160504118';


select @inf;




#Prompt information for the delete operation, cancel the current delete operation
delimiter $$
create trigger ct_table BEFORE  DELETE
    on student for each ROW
         BEGIN
             set @info1 = 'Not authorized to delete records';
         END $$
delimiter ;


begin WORK;
delete from student
   WHERE Student ID = '160504118';
ROLLBACK work;
SELECT @info1;
SELECT * from student
   WHERE Student ID = '160504118';


2. View triggers
#View trigger information
show TRIGGERS;


#View ct_student trigger
show CREATE TRIGGER ct_student;


3. Delete the trigger
#delete ct_student trigger
DROP  TRIGGER ct_student;