Thanks for reporting this, Vladimir. You can file a JIRA for it.
Best,
Chuwnei
On Wed, Aug 12, 2020 at 12:06 AM Julian Hyde <jhyde.apa...@gmail.com> wrote:
> I’m not entirely sure why RelFieldTrimmer doesn’t touch the “*” case.
> Perhaps because its main job is to trim fields, and so if there’s no field
> trimming to be done, it tries to do no harm.
>
> The main code responsible for pruning empty relational operators is
> PruneEmptyRules. I think you should apply these.
>
> Julian
>
> > On Aug 11, 2020, at 6:13 AM, Vladimir Ozerov <ppoze...@gmail.com> wrote:
> >
> > Hi colleagues,
> >
> > Consider the following query. If the RelFieldTrimmer is applied to this,
> > then the expression is reduced to an empty LogicalValues:
> > SELECT field FROM table WHERE TRUE IS FALSE
> >
> > However, the following query will not be simplified, leaving a table scan
> > with "always false" filter:
> > SELECT * FROM table WHERE TRUE IS FALSE
> >
> > After some debugging I found that the problem is in the following piece
> of
> > code in the RelFieldTrimmer:
> >
> > // If the input is unchanged, and we need to project all columns,
> > // there's nothing we can do.
> > if (newInput == input
> > && fieldsUsed.cardinality() == fieldCount) {
> > return result(filter, Mappings.createIdentity(fieldCount));
> > }
> >
> > My question - is it a known issue? Looks like this early return from the
> > method misses an important optimization opportunity. Can this check be
> > removed completely?
> >
> > Regards,
> > Vladimir
>
