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Coding the Trigger Body

That is the only problem with this technique for foreign key updates. The trigger cannot miss rows that have been changed but not committed by another transaction, because the foreign key constraint guarantees that no matching foreign key rows are locked before the after-row trigger is called.

System Trigger Restrictions

Depending on the event, different event attribute functions are available. For example, certain DDL operations may not be allowed on DDL events. Check "Event Attribute Functions" on page 10-2 before using an event attribute function, because its effects might be undefined rather than producing an error condition.

Only committed triggers are fired. For example, if you create a trigger that should be fired after all CREATE events, then the trigger itself does not fire after the creation, because the correct information about this trigger was not committed at the time when the trigger on CREATE events was fired.

For example, if you execute the following SQL statement:

CREATE OR REPLACE TRIGGER Foo AFTER CREATE ON DATABASE

BEGIN null;

END;

Then, trigger foo is not fired after the creation of foo. Oracle Database does not fire a trigger that is not committed.

Foreign Function Callouts

All restrictions on foreign function callouts also apply.

Who Is the Trigger User?

The following statement, inside a trigger, returns the owner of the trigger, not the name of user who is updating the table:

SELECT Username FROM USER_USERS;

Using Triggers 9-25

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