Re: why are these different..

Chris,

It's beginning to be late here and moreover I'm deep in (hush) MySQL, so the reason for the difference isn't immediately obvious to me, but I'd have rewritten it as

select periodID, projectNumber, changeDate, statusID

from (select p.periodID,
ps.projectNumber,
ps.changeDate,

ps.statusID,
rank() over (partition by p.periodID,
ps.projectNumber

order by ps.changeDate desc) rnk

from period p,
projectStatus ps

where ps.changeDate >= trunc( p.startDate )

and ps.changeDate < trunc(p.endDate) + 1)

where rnk = 1

No need to multiply the analytical clauses (there's some work involved behind the scene each time) and since I expect period to be much smaller than projectStatus (i.e. I don't mind scanning it) I prefer having 'trunc()' always applied to columns from period, in case I would have indexes or partitions relating to changeDate in projectStatus.

HTH Stéphane Faroult

Stephens, Chris wrote:
>
> Part of the problem is that there are multiple statusid’s associated
> with a periodid/projectnumber/changedate combo. …but there is a
> different number of rows being returned that I don’t understand.
>
> *From:* oracle-l-bounce_at_freelists.org
> [mailto:oracle-l-bounce_at_freelists.org] *On Behalf Of *Stephens, Chris
> *Sent:* Tuesday, March 11, 2008 4:06 PM
> *To:* Oracle-L Freelists
> *Subject:* why are these different..
>
> This might show my lack of sql understanding but I’m trying to rewrite
> a query to prevent an extra scan of a table. The original query looks
> like:
>
> select ps2.periodID, ps2.projectNumber, ps2.changeDate, ps3.statusID
>
> from ( select p.periodID, ps.projectNumber, max(ps.changeDate) as
> changeDate
>
> from period p, projectStatus ps
>
> where ps.changeDate >= trunc( p.startDate )
>
> and trunc( ps.changeDate ) <= p.endDate
>
> group by p.periodID, ps.projectNumber ) ps2, projectStatus ps3
>
> where ps2.projectNumber = ps3.projectNumber and ps2.changeDate =
> ps3.changeDate
>
> my attempt to rewrite:
>
> select distinct p.periodid,
>
> ps.projectnumber,
>
> first_value(ps.changedate) over (partition by p.periodid,
> ps.projectnumber order by ps.changedate desc) changedate,
>
> first_value(ps.statusid) over (partition by p.periodid,
> ps.projectnumber order by ps.changedate desc) statusid
>
> from period p,
>
> projectstatus ps
>
> where ps.changedate >= trunc(p.startdate) and
>
> trunc( ps.changeDate ) <= p.endDate
>
> the results are different though.
>
> Anyone see why they are different?
>
>
> CONFIDENTIALITY NOTICE:
> This message is intended for the use of the individual or entity to
> which it is addressed and may contain information that is privileged,
> confidential and exempt from disclosure under applicable law. If the
> reader of this message is not the intended recipient or the employee
> or agent responsible for delivering this message to the intended
> recipient, you are hereby notified that any dissemination,
> distribution or copying of this communication is strictly prohibited.
> If you have received this
> communication in error, please notify us immediately by email reply.
>
>
> CONFIDENTIALITY NOTICE:
> This message is intended for the use of the individual or entity to
> which it is addressed and may contain information that is privileged,
> confidential and exempt from disclosure under applicable law. If the
> reader of this message is not the intended recipient or the employee
> or agent responsible for delivering this message to the intended
> recipient, you are hereby notified that any dissemination,
> distribution or copying of this communication is strictly prohibited.
> If you have received this
> communication in error, please notify us immediately by email reply.

--
http://www.freelists.org/webpage/oracle-l