Need assistance in SQL query (10 years since I did SQL)

Question

Hi Guys,
I've been trying to remove some SQL rust. I haven't done SQL in a while.
Here are the tables (%=int, $ = varcchar)
RESULT
% RESULT_ID----$ RC--------------% YEAR_ID----% PERIOD_ID--% CONTRACT_NO----%Value
20841---------------1439---------------83---------------37---------------010427102---------------1
20842---------------1439---------------83---------------41---------------010427102---------------2
20843---------------1439---------------84---------------37---------------010427102---------------3
20844---------------1439---------------84---------------41---------------010427102---------------4
20845---------------1439---------------83---------------34---------------010427102---------------5
YEARS
YEAR_ID-------YEAR_DESC
83---------------2010 - 2011
84---------------2011 - 2012
PERIOD
PERIOD_ID-----PERIOD_DESC
34---------------14          
37---------------02
41---------------03
What I want is to get the last period of each year in table RESULT. (I'll work the rest of the WHERE Statement myself, because I omitted a lot of info/columns for simplicity reasons)
Note that I cannot rely on the Period ID, because chronological order is not respected.
In the above scenario I should GET
% RESULT_ID----$ RC--------% YEAR_ID-------% PERIOD_ID------% CONTRACT_NO-----%Value
20844---------------1439---------------84---------------41---------------010427102---------------4
20845---------------1439---------------83---------------34---------------010427102---------------5
I have the following but it only returns values if The year Has the last Period !
SELECT DISTINCT RESULT.RESULT_ID, RESULT.RC, RESULT.PERIOD_ID, RESULT.YEAR_ID, RESULT.CONTRACT_NO, YEARS.YEAR_DESC
FROM RESULT, YEARS
WHERE RESULT.YEAR_ID = YEARS.YEAR_ID AND -- This is my problem I want last period for each year.
RESULT.PERIOD_ID = (SELECT PERIOD_ID FROM PERIOD WHERE CAST(PERIOD_DESC AS INT) = (Select MAX(CAST(PERIOD_DESC AS INT)) from period)) ---I think this works fine i'm able to get last period
ORDER BY YEARS.YEAR_DESC;
Edited by: 935079 on May 17, 2012 11:32 AM
formatting add space not tabs
Edited by: 935079 on May 17, 2012 11:35 AM

Answer 1

Hi,
935079 wrote:
When I state "latest" it means the GREATEST PERIOD_DESC For each YEAR_ID.I see. In that case, you need to join the result and period tables in the sub-query.
I should have added that EACH CONTRACT_NO has to have a latest period for each year_id (In the above example I only one distinct contract_no)So you don't want one row of output for each distinct year_id; you want an output row for each distinct combination of contract_no and year_id. So where I originally used year_id (in the PARTITION BY clause) you'll want to both year_id and contract_no.
I think you want something like this:
WITH     got_r_num     AS
     SELECT  r.*          -- or list the columns you want
     ,     ROW_NUMBER () OVER ( PARTITION BY  r.year_id
                               ,                    r.contract_no
                               ORDER BY          p.period_id     DESC     NULLS LAST
                       ) AS r_num
     FROM    result  r
     JOIN     period     p  ON     r.period_id     = p.period_id
SELECT     *     -- or list all columns except r_num
FROM     got_r_num
WHERE     r_num     = 1
;>
There are a lot of things I don't understand in your query I will have to learn
"ROW_NUMBER ()"
"OVER"
"PARTITION BY"
"NULLS LAST"
I have no idea what these do. Thanks, Now I have some reading to do :-)ROW_NUMBER is an analytic function. You can find out more about it in the SQL language manual
http://docs.oracle.com/cd/E11882_01/server.112/e26088/functions156.htm#sthref1471
Analytic functions were new in Oracle 8.1. That version was released more than 10 years ago, but you might not have had the most recent version of Oracle at that time, so it's quite reasonable that ROW_NUMBER is new to you.
Analytic functions are extremely useful, but, I admit, the syntax ("... OVER (analytic_clasue)") is frightening at first. When reading about ROW_NUMBER, make sure you also follow the link to "Analytic Functions"
http://docs.oracle.com/cd/E11882_01/server.112/e26088/functions004.htm#i81407