Can somebody explain difference between "before" and "after" trigger in oracle 10g with an example ?
See Question&Answers more detail:osCan somebody explain difference between "before" and "after" trigger in oracle 10g with an example ?
See Question&Answers more detail:osFirst, I'll start my answer by defining trigger: a trigger is an stored procedure that is run when a row is added, modified or deleted.
Triggers can run BEFORE the action is taken or AFTER the action is taken.
BEFORE
triggers are usually used when validation needs to take place before accepting the change. They run before any change is made to the database. Let's say you run a database for a bank. You have a table accounts
and a table transactions
. If a user makes a withdrawal from his account, you would want to make sure that the user has enough credits in his account for his withdrawal. The BEFORE
trigger will allow to do that and prevent the row from being inserted in transactions
if the balance in accounts
is not enough.
AFTER
triggers are usually used when information needs to be updated in a separate table due to a change. They run after changes have been made to the database (not necessarily committed). Let's go back to our back example. After a successful transaction, you would want balance
to be updated in the accounts
table. An AFTER
trigger will allow you to do exactly that.