Editing Database trigger (section)

=== Before - statement-level trigger ===
Using a BEFORE statement trigger is particularly useful when enforcing database restrictions.<ref>{{Cite web|url=https://docs.oracle.com/cd/B28359_01/appdev.111/b28370/create_trigger.htm|title=Database PL/SQL Language Reference|website=docs.oracle.com}}</ref> This example demonstrate how to enforce a restriction upon someone named "SOMEUSER" on the table phone_book.

<syntaxhighlight lang="sql">
CREATE OR REPLACE TRIGGER hauschbc 
  BEFORE INSERT ON SOMEUSER.phone_book
BEGIN
    RAISE_APPLICATION_ERROR (
         num => -20050,
         msg => 'Error message goes here.');
END;
</syntaxhighlight>

Now, when "SOMEUSER" is logged in after attempting any INSERT this error message will show:

 SQL Error: ORA-20050: Error message goes here.

Custom errors such as this one has a restriction on what the num variable can be defined as. Because of the numerous other pre-defined errors this variable must be in the range of −20000 to −20999.