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Trigger comparing columns on UPDATE

Posted on 2007-11-15
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Last Modified: 2013-12-19
Hi Experts -
I'm trying to write an UPDATE trigger for an Oracle database.  The goal is to check an existing date column to make sure the newly updated column is later.
Here's what I have:

CREATE or REPLACE TRIGGER trigger_name
BEFORE INSERT OR UPDATE date1 ON sometable1
FOR EACH ROW
BEGIN
  IF (_______date2 < _______date1) THEN
        RAISE_APPLICATION_ERROR(-20001, Date2 must be greater than Date1);
    END IF;
END;

When I do an insert with a date2 that is before date1, the trigger is not firing.  I don't know what to put in the underlined fields above (:new., :old, etc.).

Thanks for any insight you can provide.

chezbrgrs
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Question by:chezbrgrs
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14 Comments
 
LVL 18

Expert Comment

by:Jinesh Kamdar
ID: 20289618

CREATE or REPLACE TRIGGER trigger_name
BEFORE INSERT OR UPDATE date1 ON sometable1
FOR EACH ROW
BEGIN
IF (:new.date1 < :old.date1) THEN
   RAISE_APPLICATION_ERROR(-20001, New Date must be greater than Old Date); 
END IF; 
END;

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LVL 12

Expert Comment

by:jwahl
ID: 20289683
do you have a NOT NULL constraint on date1?
if not, you have to compare with NVL() or do an additional check.


CREATE or REPLACE TRIGGER trigger_name
BEFORE INSERT OR UPDATE date1 ON sometable1
FOR EACH ROW
BEGIN
  IF :NEW.date1 < :OLD.date1 THEN
     RAISE_APPLICATION_ERROR(-20001, 'New Date must be greater than old Date!');
  END IF;
END;

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Author Comment

by:chezbrgrs
ID: 20289705
Sorry, I wasn't clear.  The dates are in two different columns (startdate and enddate).  Wouldn't this solution just be looking at one column?
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LVL 18

Expert Comment

by:Jinesh Kamdar
ID: 20289830
Then, you dont need a trigger at all. Just create a CHECK constraint on the table as below : -

ALTER TABLE sometable1 ADD CONSTRAINT someconstraint1 CHECK (start_date <= end_date) ENABLE VALIDATE;

Above would throw error if the existing data in the table does not follow the constraint rule. In that case, u may use the NOVALIDATE option to ignore validation of existing data.
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LVL 12

Expert Comment

by:jwahl
ID: 20289837
in this case you also can define a check constraint:





ALTER TABLE my_table ADD 
CONSTRAINT date_test
 CHECK (startdate < enddate) ENABLE
 VALIDATE;

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Expert Comment

by:jwahl
ID: 20289843
jinesh_kamdar is always faster ... ;-)
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LVL 18

Expert Comment

by:Jinesh Kamdar
ID: 20289895
@jwahl - Guess my TOAD works a bit faster ;-)
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LVL 12

Expert Comment

by:jwahl
ID: 20289925
... i don't think it's only the TOAD  ... ;-)
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Author Comment

by:chezbrgrs
ID: 20289993
The CHECK constraint would be much easier but I've been asked to use a TRIGGER and not alter the table.  Can it be done with a TRIGGER?
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Accepted Solution

by:
jwahl earned 500 total points
ID: 20290114
sure can it be done with trigger. is it possible to update startdate and enddate at the same time? can you update to NULL? if not, you can use


CREATE or REPLACE TRIGGER trigger_name
BEFORE INSERT OR UPDATE date1 ON sometable1
FOR EACH ROW
BEGIN
  IF :NEW.enddate < :OLD.startdate THEN
     RAISE_APPLICATION_ERROR(-20001, 'Enddate must be greater than Stardate!');
  END IF;
END;

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LVL 18

Expert Comment

by:Jinesh Kamdar
ID: 20290157
I think the IF condition should be IF :NEW.enddate < :NEW.startdate THEN
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Author Comment

by:chezbrgrs
ID: 20290166
jwahl -

Thanks I'll try this this evening and will let you know the results.  Thanks.

chezbrgrs
0
 
LVL 12

Expert Comment

by:jwahl
ID: 20290326
@jinesh_kamdar: you are right when the trigger is inserting then :OLD.startdate is null.

i think he should do different checks depending on insert/update:

...
   IF UPDATING THEN
       ....
   ELSIF INSERTING THEN
       ...
   END IF;
...
0
 

Author Comment

by:chezbrgrs
ID: 20294673
The :old value worked because startdate was not NULL.  Thanks for contributing.

chezbrgrs
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