De?ne triggers that ?re when a student drops a course, changes her major, or when her grade average drops belowa certain threshold. (For simplicity, assume that there is a function, grade_avg(), which takes a student Id and returns the student average grade.)
The action part of these triggers is uninteresting—just an insertion of a record into the log table, as we saw in earlier problems. We give an example of the last trigger.
```
CREATE TRIGGER WatchGPA
AFTER UPDATE, DELETE, INSERT ON Transcript
FOR EACH STATEMENT
WHEN (EXISTS (
SELECT StudId FROM Transcript T
WHERE grade_avg(StudId) < 3.0 ) )
INSERT INTO Log
SELECT DISTINCT StudId, grade_avg(StudId)
FROM Transcript T
WHERE grade_avg(StudId) < 3.0
```
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