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From Eric Owhadi <eric.owh...@esgyn.com>
Subject RE: question on normalization
Date Mon, 14 Dec 2015 21:53:36 GMT
It would be simple for pushdown to transform back to != when we are about to
turn it to a scan predicate push down.
Is it worth doing it? Or too small of an optimization?
Eric


-----Original Message-----
From: Qifan Chen [mailto:qifan.chen@esgyn.com]
Sent: Monday, December 14, 2015 3:41 PM
To: dev <dev@trafodion.incubator.apache.org>
Subject: Re: question on normalization

yes, if you turn off range spec, the != remains un-transformed.

Thanks --Qifan

On Mon, Dec 14, 2015 at 3:36 PM, Dave Birdsall <dave.birdsall@esgyn.com>
wrote:

> I don't know for sure, but I'll speculate that histogram estimation
> and RangeSpec processing in the compiler like to think in terms of
> intervals.
>
> -----Original Message-----
> From: Hans Zeller [mailto:hans.zeller@esgyn.com]
> Sent: Monday, December 14, 2015 1:35 PM
> To: dev <dev@trafodion.incubator.apache.org>
> Subject: Re: question on normalization
>
> Hi Eric, yes, the logic may be unconditional, since at the time when
> we do these transformations, we don't know yet whether the predicate
> is used in an alternate index or not, and since the overhead of the
> extra predicate is probably small.
>
> Hans
>
> On Mon, Dec 14, 2015 at 1:31 PM, Eric Owhadi <eric.owhadi@esgyn.com>
> wrote:
>
> > Sorry should have said that "an" is not a key column. So any logic
> > around MDAM should not apply.
> > Eric
> >
> > -----Original Message-----
> > From: Hans Zeller [mailto:hans.zeller@esgyn.com]
> > Sent: Monday, December 14, 2015 3:30 PM
> > To: dev <dev@trafodion.incubator.apache.org>
> > Subject: Re: question on normalization
> >
> > Hi Eric, this is probably to get usable key predicates. "an <> 1" is
> > not a key range we could use, but "an < 1" and "an > 1" make two
> > disjuncts for an MDAM scan.
> >
> > Hans
> >
> > On Mon, Dec 14, 2015 at 1:25 PM, Eric Owhadi <eric.owhadi@esgyn.com>
> > wrote:
> >
> > > I am implementing predicate push down enhancement. doing so, I
> > > found something weird.
> > >
> > > If I do select an from t132 where an != 1
> > >
> > > The normalized predicate is ((an < 1) or <an >1))
> > >
> > > I would have expected a simple an <> 1
> > >
> > > There is probably a reason being this? But what is it?
> > >
> > > Thanks in advance for the help,
> > > Eric
> > >
> >
>



--
Regards, --Qifan

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