Differences between storedprocedures and triggers
1. When you create a trigger you have to identify event and action of your trigger but when you create s.p you don't identify event and action
2.Trigger is run automatically if the event is occured but s.p don't run automatically but you have to run it manually
3. Within a trigger you can call specific s.p but within a sp you cannot call atrigger
4.Trigger execute implicitly whereas store procedure execute via procedure call from another block.
5.We can call a stored procedure from front end (.asp files, .aspx files, .ascx files etc.) but we can't call a trigger from these files.
6. Stored procedure can take the input parameters, but we can't pass the parameters as an input to a trigger.
We can create a trigger to update the 'product_price_history' table when the price of the product is updated in the 'product' table.
1) Create the 'product' table and 'product_price_history' table
CREATE TABLE product_price_history
(product_id number(5),
product_name varchar2(32),
supplier_name varchar2(32),
unit_price number(7,2) );
CREATE TABLE product
(product_id number(5),
product_name varchar2(32),
supplier_name varchar2(32),
unit_price number(7,2) );
2) Create the price_history_trigger and execute it.
CREATE or REPLACE TRIGGER price_history_trigger
BEFORE UPDATE OF unit_price
ON product
FOR EACH ROW
BEGIN
INSERT INTO product_price_history
VALUES
(:old.product_id,
:old.product_name,
:old.supplier_name,
:old.unit_price);
END;
/
3) Lets update the price of a product.
UPDATE PRODUCT SET unit_price = 800 WHERE product_id = 100
Once the above update query is executed, the trigger fires and updates the 'product_price_history' table.
4)If you ROLLBACK the transaction before committing to the database, the data inserted to the table is also rolled back.