Please find me a better sql

Question

Say I have a table TBL_PROJECT. Projects can have different status - Active, Hold, Complete
Project_ID
Descritption
Latest Status
Target Completion Date
1
Project A
Active
12/20/2013
2
Project B
Hold
03/04/2014
3
Project C
Complete
10/30/2013
Say I have an another tabel TBL_TRACK_STATUS which tracks the status change of the projects.
Project_ID
Status
Changed_Date
1
Active
01/20/2013
1
Hold
05/05/2013
1
Active
10/05/2013
2
Active
04/06/2013
2
Hold
08/08/2013
3
Active
02/10/2013
3
Complete
10/15/2013
Now I need a query that will get me result like below
Project_ID
Description
Active Date
Hold Date
Complete Date
1
Project A
10/05/2013
05/05/2013
2
Project B
04/06/2013
08/08/2013
3
Project C
02/10/2013
10/15/2013
Well, I can write the query as below:
SELECT A.PROJECT_ID,
  A.DESCRIPTION,
  (SELECT MAX(B.CHANGED_DATE)
  FROM TBL_TRACK_STATUS B
  WHERE A.PROJECT_ID = B.PROJECT_ID
  AND B.STATUS       = 'Active'
  ) AS "Active Date",
  (SELECT MAX(C.CHANGED_DATE)
  FROM TBL_TRACK_STATUS C
  WHERE A.PROJECT_ID = C.PROJECT_ID
  AND C.STATUS       = 'Hold'
  ) AS "Hold Date",
  (SELECT MAX(D.CHANGED_DATE)
  FROM TBL_TRACK_STATUS D
  WHERE A.PROJECT_ID = D.PROJECT_ID
  AND D.STATUS       = 'Complete'
  ) AS "Complete Date"
FROM TBL_PROJECT A;
OR
I can write the functions that will return the status date changed -
SELECT A.PROJECT_ID,  -- ASSUMING THE FUNCTIONS RETURNS THE DATE FOR DIFFERENT STATUSES
  GET_ACTIVE_DATE_CHANGED(A.PROJECT_ID)   AS "Active Date",
  GET_HOLD_DATE_CHANGED(A.PROJECT_ID)     AS "Hold Date",
  GET_COMPLETE_DATE_CHANGED(A.PROJECT_ID) AS "Complete Date"
FROM TBL_PROJECT A;
My question is - IS THERE ANY OTHE WAY THAT THE QUERY CAN BE WRITTEN IN EFFICIENT MANNER THAN WHAT I AM DOING HERE?

Answer 1

You could consider analytics ...
This query is untested, but it should give you the idea:
with w_base as (
      select p.project_id, p.description,
               max(case when status = 'Active' then t.changed_date else null end)
                     over (partition by t.project_id
                           order by case when status = 'Active' then t.changed_date else null end nulls last ) active_date,
               max(case when status = 'Hold' then t.changed_date else null end)
                     over (partition by t.project_id
                           order by case when status = 'Hold' then t.changed_date else null end nulls last ) hold_date,
               max(case when status = 'Complete' then t.changed_date else null end)
                     over (partition by t.project_id
                           order by case when status = 'Complete' then t.changed_date else null end nulls last ) complete_date,
             row_number() over (partition by p.project_id order by t.changed_date) rnum
        from tbl_project p,
             tbl_track_status t
       where p.project_id = t.project_id
select project_id, description, active_date, hold_date, complete_date
  from w_base
where rnum = 1