MySQL project 7 Summary

Create and use triggers
trigger （TRIGGER） yes MySQL One of the database objects , from 5.0.2 Version starting support . This object is very similar to a function in a programming language , All need to be stated 、 Execution, etc . But the execution of the trigger is not called by the program , It's not started by hand , It's triggered by events 、 Activate to execute . It's kind of similar DOM In the event .
So why use database object triggers ？ In the specific development project , The following examples are often encountered ：

<1> Have the field student name in the student table , Total field students , Whenever you add a student message , The total number of students must be changed at the same time .

<2> There will also be abbreviations of students' names in the student list , Student address and other fields , When adding student information , It is often necessary to check the telephone 、 Whether the format of e-mail is correct .

The above example has such characteristics when it is completed with triggers , When the table changes , Do some processing automatically .MySQL It's triggering DELETE/UPDATE/INSERT Statement will automatically execute the set operation , other SQL Statement does not activate the trigger .
Create trigger
Use the help command to view the specific syntax ：

CREATE

[DEFINER = { user | CURRENT_USER }]

TRIGGER trigger_name

trigger_time trigger_event

ON tbl_name FOR EACH ROW

trigger_body

In the syntax

trigger_name： Trigger name , Cannot be repeated with an existing trigger ;
trigger_time：{ BEFORE | AFTER }, Means to trigger before or after an event ;
trigger_event:：{ INSERT |UPDATE | DELETE }, The specific event that triggers the trigger ;
tbl_name： The trigger acts on tbl_name On ;

View and delete triggers
Check triggers

SHOW TRIGGERS Statement view trigger information

SHOW TRIGGERS;

stay triggers See trigger information in table
Delete trigger

DROP TRIGGER Trigger Name ;

DROP TRIGGER trig_book ;

DROP TRIGGER trig_book2