Please can someone help me to build a query

Question

Please can someone help me to build a query for getting the following results. I work with Oracle 9.
My data is about this:
Projectid / Activitycode / Act.DS / Earlystart / ActualStart
{color:#ff0000}P001 / 110M / blabla / 1-1-08 / 1-1-08{color}
{color:#3366ff}P001 / 230M / fdsfds / 31-1-09 / null{color}
P001 / 450M / fsfsd / 1-4-09 / null
P002 / null / null / 1-12-08 / 1-12-08
{color:#3366ff}P002 / 110M / nhggh / 5-2-09 / null{color}
P002 / 750M / wdwdwd / 5-2-09 / null
P002 / 210M / plplplp / 31-12-08 / 31-12-08
{color:#ff0000}P002 / 550M / ewdwd / 5-1-09 / null{color}
I'd like to get one row for each Projectid with the {color:#3366ff}first next Early- or Actualstart{color} {color:#3366ff}after today{color} and one row with the {color:#ff0000}latest early-/actualstart before today{color}. When there are two or more rows with the same date then I want the first (minimum) Activitycode. This last condition makes it insoluble for me!
I've tryed SQL with nested Select-statements in the Where-clause. But I've got still 2 rows per projectid because I select the min(nvl(Earlystart ,ActualStart ) I've tryed SQL with an Select in the FROM-claus with Partion BY, but I can't get it work right.
Can someone show me the right way to solve my problem?

Answer 1

How's this?
with my_tab as (select 'P001' projectid,
                       '110M' activitycode,
                       'blabla' act_ds,
                       to_date('01/01/2008', 'dd/mm/yyyy') earlystart,
                       to_date('01/01/2008', 'dd/mm/yyyy') actualstart
                from   dual
                union all
                select 'P001' projectid,
                       '230M' activitycode,
                       'fdsfds' act_ds,
                       to_date('31/01/2009', 'dd/mm/yyyy') earlystart,
                       null actualstart
                from   dual
                union all
                select 'P001' projectid,
                       '450M' activitycode,
                       'fsfsd' act_ds,
                       to_date('01/04/2009', 'dd/mm/yyyy') earlystart,
                       null actualstart
                from   dual
                union all
                select 'P002' projectid,
                       null activitycode,
                       null act_ds,
                       to_date('01/12/2008', 'dd/mm/yyyy') earlystart,
                       to_date('01/12/2008', 'dd/mm/yyyy') actualstart
                from   dual
                union all
                select 'P002' projectid,
                       '110M' activitycode,
                       'nhggh' act_ds,
                       to_date('05/02/2009', 'dd/mm/yyyy') earlystart,
                       null actualstart
                from   dual
                union all
                select 'P002' projectid,
                       '750M' activitycode,
                       'wdwdwd' act_ds,
                       to_date('05/02/2009', 'dd/mm/yyyy') earlystart,
                       null actualstart
                from   dual
                union all
                select 'P002' projectid,
                       '210M' activitycode,
                       'plplplp' act_ds,
                       to_date('31/12/2008', 'dd/mm/yyyy') earlystart,
                       to_date('31/12/2008', 'dd/mm/yyyy') actualstart
                from   dual
                union all
                select 'P002' projectid,
                       '550M' activitycode,
                       'ewdwd' act_ds,
                       to_date('05/01/2009', 'dd/mm/yyyy') earlystart,
                       null actualstart
                from   dual)
-- above mimics your table; main query is below:
select mt2.projectid,
       mt2.activitycode,
       mt2.act_ds,
       mt2.earlystart,
       mt2.actualstart
from   (select mt.projectid,
               mt.activitycode,
               mt.act_ds,
               mt.earlystart,
               mt.actualstart,
               mt.date_col,
               mt.before_after_today,
               row_number() over (partition by mt.projectid, mt.before_after_today
                                  order by mt.date_col asc) rn_after,
               row_number() over (partition by mt.projectid, mt.before_after_today
                                  order by mt.date_col desc) rn_before
        from   (select projectid,
                       activitycode,
                       act_ds,
                       earlystart,
                       actualstart,
                       coalesce(actualstart, earlystart, to_date('01/01/4000', 'dd/mm/yyyy')) date_col,
                       case when coalesce(actualstart,
                                          earlystart,
                                          to_date('01/01/4000', 'dd/mm/yyyy')) <= trunc(sysdate) then 1
                            else 2
                       end before_after_today
                from   my_tab) mt) mt2,
        (select 1 id, 1 col_id from dual union all
         select 1 id, 2 col_id from dual) dummy
where  dummy.id = case when mt2.before_after_today = 1 then rn_before
                       else rn_after
                  end
and    mt2.before_after_today = dummy.col_id
PROJECTID     ACTIVITYCODE     ACT_DS     EARLYSTART     ACTUALSTART
P001     110M     blabla     01/01/2008     01/01/2008
P001     230M     fdsfds     31/01/2009     
P002     550M     ewdwd     05/01/2009     
P002     110M     nhggh     05/02/2009