Create After Update Trigger in SQL

After Trigger in SQL is fired before update the column in the table.

Understand with Example

The Tutorial illustrate an example from 'Create After Update Trigger in SQL'. In order to understand this example, we create a table Stu_Table and Stu_Log. To create these tables we use create table statement that construct table Stu_Table and Stu_Log with specific field name and data type respectively.

Create Table Stu_Table

Create Table Stu_Table( Stu_Id int, Stu_Name varchar(15),Stu_Class int);

Create Table Stu_Log

create table stu_log( user_id VARCHAR(15), description VARCHAR(100));

Create Trigger Stu_Update

The below Query create a Trigger 'stu_update' on table stu_table.

delimiter $$

CREATE TRIGGER stu_update

AFTER UPDATE ON stu_table FOR EACH ROW
BEGIN
	INSERT into stu_log(user_id, description)
        VALUES (user(), CONCAT('Update Student Record 
        (',old.stu_id,' ',old.stu_name,' ',old.stu_class,
	') to (',new.stu_id,' ',new.stu_name,' ',new.stu_class,')'));
END$$
delimiter ;

Insert Data Into Stu_Table

insert into stu_table values(1, 'Komal',10);
insert into stu_table values(2, 'Ajay',10);
insert into stu_table values(3, 'Santosh',10);
insert into stu_table values(4, 'Rakesh',10);
insert into stu_table values(5, 'Bhau',10);

Stu_Table

+--------+----------+-----------+
| Stu_Id | Stu_Name | Stu_Class |
+--------+----------+-----------+
| 1      | Komal    | 10        |
| 2      | Ajay     | 10        |
| 3      | Santosh  | 10        |
| 4      | Rakesh   | 10        |
| 5      | Bhau     | 10        |
+--------+----------+-----------+

Update Stu_Table

update stu_table set Stu_Class = stu_class+1;

Stu_Table

+--------+----------+-----------+
| Stu_Id | Stu_Name | Stu_Class |
+--------+----------+-----------+
| 1      | Komal    | 11        |
| 2      | Ajay     | 11        |
| 3      | Santosh  | 11        |
| 4      | Rakesh   | 11        |
| 5      | Bhau     | 11        |
+--------+----------+-----------+

Stu_Log

+----------------+--------------------------------------------------------+
| user_id        | description                                            |
+----------------+--------------------------------------------------------+
| root@localhost | Update Student Record (1 Komal 11) to (1 Komal 12)     |
| root@localhost | Update Student Record (2 Ajay 11) to (2 Ajay 12)       |
| root@localhost | Update Student Record (3 Santosh 11) to (3 Santosh 12) |
| root@localhost | Update Student Record (4 Rakesh 11) to (4 Rakesh 12)   |
| root@localhost | Update Student Record (5 Bhau 11) to (5 Bhau 12)       |
+----------------+--------------------------------------------------------+

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