The below example shows how Trigger's can enter into cyclic cascading. 2) The UPDATE Trigger, trigger B on table 'xyz' issues an INSERT on table 'abc'.In such a situation, when there is a row inserted in table 'abc', trigger A fires and will update table 'xyz'.4)If you ROLLBACK the transaction before committing to the database, the data inserted to the table is also rolled back.
For Example: The price of a product changes constantly.
It is important to maintain the history of the prices of the products.
For Example: Let's create a table 'product_check' which we can use to store messages when triggers are fired.
Let's create a BEFORE and AFTER statement and row level triggers for the product table.
This can be useful for example when you want to write a history record, but you don't want to do it if nothing really changed.
We use this all the time in ETL importing processes where we may re-import data but if nothing really changed in the source file we don't want to create a new history record.
You can compare the values in these tables to see if your field value was actually changed.
Here's a quick way to scan the rows to see if ANY column changed before deciding to run the contents of 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 Once the above update query is executed, the trigger fires and updates the 'product_price_history' table.
Within the trigger, you have access to two internal tables that may help.