Re: Triggers on columns

Peter Eisentraut <peter_e(at)gmx(dot)net> wrote:

> Therefore, it cannot be completely unexpected if column triggers are
> called even if the column was not actually changed in a semantically
> significant way.

Ok, the attached patch implements standard-compliant version of
column trigger.

Retrieving modified columns is not so difficult as I expected.
It is in:
rt_fetch(relinfo->ri_RangeTableIndex, estate->es_range_table)->modifiedCols
and the information are passed from caller to trigger routines.

However, to be honest, I think standard-compliant column trigger is
useless... I'm thinking additional extension for triggers -- if we
want to check modifications of actual values, it could be defined as:

CREATE TRIGGER trig BEFORE UPDATE ON tbl FOR EACH ROW
WHEN (NEW.col <> OLD.col) EXECUTE PROCEDURE trigger_func();

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center