Mysql -- trigger operation, Mysql -- trigger operation

Mysql -- trigger operation, Mysql -- trigger operation
1. Why should I use a trigger?

2. Create a trigger 2.1 create a trigger with an execution statement

Example: There are two table objects in the database company: The Department table (t_dept) and the diary table (t_diary). When you create a trigger to insert a record to the Department table, the current time will be inserted into the diary table before insertion.

Department table:

　　　

Diary table:

Create a trigger:

Insert record:

Result: an additional record is added to the diary table.

2.2 create a trigger containing multiple execution statements

Syntax:

　　　　

Example:

When a trigger is created to insert records into a department table, two records are inserted into the diary table.

Code Analysis:

　　　　

Insert a record:

Result: There are two more records in the diary table:

3. view TRIGGER 3.1 view TRIGGER through show trigger statement

Syntax:

Example:

3.2 view the trigger by viewing the system table trigger

In Mysql, there is a system table triggers in the information_schema of the system database that stores all the trigger information. Therefore, you can query records in this table to view the trigger. The table structure is as follows:

　　

 

View method:

View All triggers:

View the specified trigger:

4. delete a TRIGGER 4.1 delete a TRIGGER using the drop trigger statement

Syntax:

Example :"