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<h1>More trigger hints</h1>

<p>
The code fragments given here are incomplete and some vital parts are missing
(on purpose!).
However, if you're stuck you might find it useful to study these code fragments.
</p>

<hr>

<pre>
CREATE OR REPLACE TRIGGER CourseRegistration
INSTEAD OF INSERT ON Registrations
REFERENCING NEW AS new
FOR EACH ROW
DECLARE
hasPassed Int;
BEGIN
   SELECT COUNT (*) INTO hasPassed FROM PassedCourses 
     WHERE course  = :new.course AND student = :new.student;
   IF hasPassed > 0 THEN 
     RAISE_APPLICATION_ERROR(-20001,'Student has already passed');
   ELSE
     RAISE_APPLICATION_ERROR(-20002,'Student has not passed course! This should not be an actual error...');
   END IF;
END;
</pre>

<hr>

<h3>Trigger compilation errors</h3>

<p>
If your trigger is "created with compilation errors", you can get
additional information about the errors by typing:
</p>
<pre>
    SHOW ERRORS;
</pre>
<p>
See Ullman's notes on
<a href="http://infolab.stanford.edu/~ullman/fcdb/oracle/or-triggers.html#displaying%20trigger%20definition%20errors">displaying trigger definition errors</a>.
</p>

<hr>

Last Modified:  7 December 2015
by Jonas Duregård

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