Re: Re: Removing unneeded self joins

On Mon, Jul 15, 2024 at 2:08 PM Andrei Lepikhov <lepihov(at)gmail(dot)com> wrote:
>
> On 7/15/24 12:31, jian he wrote:
> > hi.
> > Here is the latest patch (v6),
> > I've made the following changes.
> >
> > * disallow original Query->resultRelation participate in SJE.
> > for SELECT, nothing is changed. for UPDATE/DELETE/MERGE
> > we can do:
> > EXPLAIN (COSTS OFF)
> > UPDATE sj sq SET b = sq.b + sz.a FROM (select s1.* from sj s1 join sj
> > s2 on s1.a = s2.a) as sz
> > WHERE sz.a = sq.a;
> >
> > here, only "(select s1.* from sj s1 join sj s2 on s1.a = s2.a)" can
> > apply to SJE.
> >
> > but for now we cannot apply SJE to
> > EXPLAIN (COSTS OFF)
> > UPDATE sj sq SET b = sq.b + sz.a FROM sj as sz WHERE sz.a = sq.a;
> >
> > so the EPQ abnormality issue[1] won't happen.
> >
> >
> > * add a new function: ChangeVarNodesExtended for
> > address concerns in [2]
> I see you still stay with the code line:
> if (omark && imark && omark->markType != imark->markType)
>
> It is definitely an error. What if omark is NULL, but imark is not? Why
> not to skip this pair of relids? Or, at least, insert an assertion to
> check that you filtered it earlier.
>

i think "omark is NULL, but imark is not" case won't reach to
remove_self_joins_one_group.
In that case, omark associated RangeTblEntry->rtekind will be RTE_SUBQUERY,
and will be skipped earlier in remove_self_joins_recurse.

Still, do you think the following code is the right way to go?

if ((omark == NULL && imark != NULL) ||
(omark != NULL && imark == NULL) ||
(omark && imark && omark->markType != imark->markType))
continue;