Trigger set insert row values to null [closed] - sql

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So I'm trying to write a trigger that when something is inserted into the database if it is over a specific time set the row values to null
CREATE OR REPLACE TRIGGER hi
AFTER INSERT OR UPDATE OF CLASS_TIME ON class
FOR EACH ROW
BEGIN
IF (:NEW.CLASS_TIME < '09:00' )
OR (:NEW.CLASS_TIME > '18:00' )
THEN
RAISE_APPLICATION_ERROR(-20000, 'Due to low attendance no class cannot be scheduled at that time');
SET NEW.STAFFNO = NULL;
SET NEW.CLASS_DAY = NULL;
SET NEW.CLASS_TYPE = NULL;
SET NEW.ROOMNUM = NULL;
END IF;
END;
All that I have found online shows that what Ive got is correct but I get the error on the STAFFNO. Thanks in advance for any input.

Answer 1

First of all you have to decide:
either you want the insert or update to fail when it's being done at undesired time
or you want the insert or update to be processed, but with the columns set to null then.
You cannot have both.
In case you want to set the columns to NULL, this should be a BEFORE INSERT/UPDATE trigger, so the changed columns get written to the table. (In an AFTER INSERT/UPDATE trigger setting the fields to some value would not have any effect, becase they are not written.)
Then SET NEW.STAFFNO = NULL; is no valid PL/SQL, that would have to be :NEW.STAFFNO := NULL; instead.
CREATE OR REPLACE TRIGGER hi
BEFORE INSERT OR UPDATE OF class_time ON class
FOR EACH ROW
WHEN (new.class_time NOT BETWEEN '09:00' AND '18:00')
BEGIN
:new.staffno := null;
:new.class_day := null;
:new.class_type := null;
:new.roomnum := null;
END;