mysql-- trigger - examples

data preparation:

create table employee ( num int(50),
                        d_id int(50),
                        name varchar(50),
                        age int(50),
                        sex varchar(50),
                        homeadd varchar(50)
                       );


insert into employee values(1,1001,'zhangsan ' , 26 is , ' NaN3 ' , ' Beijing ' );
 INSERT  INTO Employee values ( 2 , 1001 , ' Lisi ' , 24 , ' NV ' , ' hunan ' );
 INSERT  INTO Employee values ( . 3 , 1002 , ' wangwu ' , 25 , ' NaN3 ' ,'jiangsu');
insert into employee values(4,1004,'aric',15,'nan','yingguo');


select * from employee;



create table department ( d_id int(50),
                          d_name varchar(50),
                          functione varchar(50),
                          address varchar(50)
                        );


insert into department values(1001,'keyanbu','yanfachanpin','3lou5hao');
insert into department values(1002,'shengchanbu','shengchanchanp','5louyiceng');
insert into department values(1003,'xiaoshoubu','cehuaxiaoshou','1louxiaoshoudating');


select * from department;

select * from employee;

 

 select * from department;

 

 

==========================================================================

the Create  the Trigger trigger name the before | the After trigger event
 on the table name for the each Row 

execute the statement; 

------------------------------- --------------------------------------------- 

DELIMITER && 
the Create  the trigger trigger is the name of the before | the After trigger event
 on the table name for the each Row
   the begin 
        execution of a statement list 
  End 
  && 
DELIMITER; 


triggering event is the trigger conditions, including INSERT, Update , the Delete ; 

table name refers to the name of the table the trigger event operations;

Create a table:

create table trigger_time ( exec_time varchar(50)
                          );



select * from trigger_time;



----------select now();

 

 

 

 

 

=================================================

Create a trigger:

create  trigger dept_trig1 before insert on department for each row insert into trigger_time values ( now() );

 

 

 

===========================================

To demonstrate, first delete a record, and then added to it:

delete from department where d_id = 1003;

 

 

 

 

 

=========================================

Add just deleted records:

insert into department values(1003,'xiaoshoubu','cehuaxiaoshou','1louxiaoshoudating'); 

 

 

 

 

 

===================================================================

在department表insert时，触发器会被触发，我们查看下：

select * from trigger_time;

 

 

===========================================================

==========================================================

 

示例02：

创建第二个演示示例用的时间表：

create table trigger_time1 ( exec_time varchar(50)
                          );


select * from trigger_time1;

 

 

 

 

==================================================================

 

创建第二个触发器：

delimiter &&
create  trigger dept_trig2 after delete on department for each row 
begin
      insert into trigger_time1 values ( now() );
      insert into trigger_time values ( now() );
end 
&&
delimi

 

 

 

 

 

 

 

 

================================================

执行删除语句：

delete from department where d_id = 1003;

 

 

 

 

 

 

==========================================

查看被删除记录的表以及2个时间表：

select * from department;
select * from trigger_time;
select * from trigger_time1;

 

 

 

 

 

 

 

 

 

=================================================================================================

查看触发器

1、查看数据库中所有触发器的信息：

       show triggers;

 

 

 

 

 

========================================================================

 

 

 

2、在triggers表中查看触发器信息

mysql中所有触发器的定义都存在information_schema数据库下的triggers表中，查询triggers表，可以查询数据库中所有触发器的详细信息

select * from information_schema.triggers; /*查询所有*/

select * from information_schema.triggers where trigger_name = 'dept_trig1'; /*单个指定查询*/

注意：在激活触发器时，对触发器中的执行语句存在一些限制。而且触发器有问题，会阻止程序向下执行，而且数据不能回滚。

select * from information_schema.triggers; /*查询所有*/

select * from information_schema.triggers where trigger_name = 'dept_trig1'; 

select * from information_schema.triggers where trigger_name = 'dept_trig2'; 

 

 

 

 

 

 

 

 

==================================================

 

3、删除触发器

     drop trigger 触发器名；

 

select * from information_schema.triggers;


drop trigger dept_trig1;

drop trigger dept_trig2;