SQL trigger to forbid deleting data newer than 2 weeks - postgresql

Question

I need help with creating a trigger which forbids user to delete data that is newer than 2 weeks.
My current code:
CREATE OR REPLACE FUNCTION f_delete_data() RETURNS trigger AS $$
BEGIN
RAISE EXCEPTION 'Cant delete data which is newer than 2 weeks.';
RETURN NULL;
END;
$$ LANGUAGE plpgsql;
CREATE TRIGGER trig_delete_data BEFORE DELETE ON Results
FOR EACH ROW WHEN (OLD.Date < DATE_SUB(NOW(), INTERVAL 14 DAY)) EXECUTE PROCEDURE
f_delete_data();
This code says there's a syntax error at or near 14 ..
Why is the date_sub(..,interval 14 day) not working?
I'm using PostgreSQL 9.3.0.

Answer 1

Why isn't the date_sub(..,intercval 14 day) not working?
$$ LANGUAGE plpgsql; indicates you're using postgres however DATE_SUB is a MySQL specific function not available in postgres.
Try replacing DATE_SUB with this
(OLD.Date < NOW() - INTERVAL '14 DAYS')

Answer 2

Besides the obvious mistake (no DATE_SUB in Postgres), you also have your logic backwards. If you want to protect rows where the value in the date column is less than 2 weeks old: "newer than 2 weeks", then you must revert the comparison operator.
CREATE TRIGGER trig_delete_data
BEFORE DELETE ON results
FOR EACH ROW
WHEN (OLD.date < DATE_SUB(NOW(), INTERVAL 14 DAY))
WHEN (OLD.date < now() - interval '14 days')
WHEN (OLD.date > now() - interval '14 days')
EXECUTE PROCEDURE f_delete_data();
And f_delete_data() really should be name something like f_protect_new_data().
Or, if your columns is an actual date like the ill-chosen column name suggests, further simplify:
WHEN (OLD.date >= CURRENT_DATE - 14)
The manual on CURRENT_DATE & friends.
Use >= in this case, the 14th day back from today is still illegal according to your definition. The bound is logically a bit different from timestamp handling.
Why "ill-chosen"? "date" is a reserved word in standard SQL and a basic type name in Postgres. If the column actually holds a timestamp, not a date, it's misleading on top of that.