Trigger and Procedure in MySql

MySQL Triggers:Auto-generate additional information in the database

TRIGGER:
A trigger is a database object that is attached to a table. In many aspects it is similar to a stored procedure. As a matter of fact, triggers are often referred to as a "special kind of stored procedure." The main difference between a trigger and a stored procedure is that the former is attached to a table and is only firedwhen an INSERT, UPDATE or DELETE occurs. You specify the modification action(s) that fire the trigger when it is created. 



NOW QUERY WILL BE:

DELIMITER $$
create trigger before_student_update BEFORE update ON student_04
for each row Begin
insert into trigger_demo set action='UPDATE',date_time=now(),phone_no=OLD.phone_no;
END;
$$
DELIMITER ;

DROP TRIGGER

The general syntax of DROP TRIGGER is :
        DROP TRIGGER trigger_name

PROCEDURE:
A stored procedure or in simple a proc is a named PL/SQL block which performs one or more specific task. This is similar to a procedure in other programming languages. A procedure has a header and a body. The header consists of the name of the procedure and the parameters or variables passed to the procedure. The body consists or declaration section, execution section and exception section similar to a general PL/SQL Block.

We can pass parameters to procedures in three ways.
1) IN-parameters
2) OUT-parameters
3) IN OUT-parameters

A procedure may or may not return any value.

CREATE [OR REPLACE] PROCEDURE proc_name [list of parameters] 

IS    

   Declaration section 

BEGIN    

   Execution section 

EXCEPTION    

  Exception section 

END; 

IS - marks the beginning of the body of the procedure and is similar to DECLARE in anonymous PL/SQL Blocks. The code between IS and BEGIN forms the Declaration section.

The syntax within the brackets [ ] indicate they are optional. By using CREATE OR REPLACE together the procedure is created if no other procedure with the same name exists or the existing procedure is replaced with the current code.