Re: trouble with sql
- From: Stephane Faroult <sfaroult@xxxxxxxxxxxx>
- To: chris_stephens@xxxxxxxxxxxx
- Date: Wed, 03 Jan 2007 22:43:12 +0100
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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