Re: trouble with sql

From: Stephane Faroult <sfaroult_at_roughsea.com>
Date: Wed, 03 Jan 2007 22:43:12 +0100
Message-ID: <459C2370.6000606@roughsea.com>

Chris,

  The other solution is to use an analytical function - or to use max() as an analytical function,
eg

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

                   max(ps.changeDate) over (partition by projectNumber) 
as maxchangeDate,
                   changeDate,
                   statusID
          from projectStatus) ps,
        period p

where ps.changeDate = ps.maxChangeDate

   and ps.changeDate between trunc(p.startDate) and trunc(p.endDate + 1) - 1/86400

Also, be careful about your comparison with the period table - especially your trunc() that are applied in one case to a column from one table, and in the other case to a column from the other table. This doesn't help with joins, although in this particular case it may not matter much.
 But your solution is not necessarily bad. It really depends on how data is stored. However, if, as can be expected, (projectNumber, changeDate) is the PK of the projectStatus table, the analytical function can be cheaply evaluated.

HTH Stephane Faroult

Stephens, Chris wrote:
> There has got to be a way to do this but I can't find the syntax.
>
> Essentially I need the max of column 3 grouped by column 1 and 2 and
> also the value of column 4 that corresponds to the returned columns
> 1,2, and 3.
>
> Here is the actual sql that I believe to be using an unnecessary join:
> 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
>
> Is there a better way to write this?
>
>
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Received on Wed Jan 03 2007 - 15:43:12 CST