Question

Hi im working on a trigger that will not allow inserts/updates when the newly inserted data (address, listnumber, date, price) has a similar tuple.

Condition – a listing cannot be listed twice on the same day
table
123, jun 19 1992
123, jun 20 1990
insert: 123, Jun 20 1990 – wouldnt work already in table

The only problem with my code is that i cant get it work when my list table has no data to begin with

create or replace TRIGGER same_prop_listed BEFORE INSERT OR UPDATE  ON HasListing
FOR each ROW
DECLARE
    c_date VARCHAR2(20);
BEGIN
    SELECT LISTING_DATE
    INTO c_date
    FROM HasListing
    WHERE PROP_ADDRESS = :NEW.prop_address;
    IF (c_date = :NEW.listing_date) THEN
    RAISE_APPLICATION_ERROR(-20001,'Cannot list same property twice in  one day!');
    END IF;
    EXCEPTION
    WHEN NO_DATA_FOUND THEN
        RAISE_APPLICATION_ERROR(-20003,'No DATA');

END;

This is in oracle.
So my errors are on – IF (c_date = :NEW.listing_date) because c_date is null

Answer 1

Why don’t you just put a multiple column unique constraint ?

ALTER TABLE YOUR_TABLE ADD CONSTRAINT UNI_CONSTR UNIQUE (COL1, COL2,
COL3);

?