Re: Virtual generated columns

On Wed, 4 Sept 2024 at 09:40, Peter Eisentraut <peter(at)eisentraut(dot)org> wrote:
>
> On 21.08.24 12:51, Dean Rasheed wrote:
> >>
> > Well what I was thinking was that (in fireRIRrules()'s final loop over
> > relations in the rtable), if the relation had any virtual generated
> > columns, you'd build a targetlist containing a TLE for each one,
> > containing the generated expression. Then you could just call
> > ReplaceVarsFromTargetList() to replace any Vars in the query with the
> > corresponding generated expressions.
>
> Here is an implementation of this. It's much nicer! It also appears to
> fix all the additional test cases that have been presented. (I haven't
> integrated them into the patch set yet.)
>
> I left the 0001 patch alone for now and put the new rewriting
> implementation into 0002. (Unfortunately, the diff is kind of useless
> for visual inspection.) Let me know if this matches what you had in
> mind, please. Also, is this the right place in fireRIRrules()?

Yes, that's what I had in mind except that it has to be called from
the second loop in fireRIRrules(), after any RLS policies have been
added, because it's possible for a RLS policy expression to refer to
virtual generated columns. It's OK to do it in the same loop that
expands RLS policies, because such policies can only refer to columns
of the same relation, so once the RLS policies have been expanded for
a given relation, nothing else should get added to the query that can
refer to columns of that relation, at that query level, so at that
point it should be safe to expand virtual generated columns.

Regards,
Dean