SQL to group the records and apply logic to pick one record from each group

Question

Hi Friends,
I am looking for a query to group the records on certain columns in a table and then from each group I want to pick only one record based on certain rules.
May be having data laid out will make my point more clear to you. Here you go :
CREATE TABLE AD_LIST
  FILE_NAME             VARCHAR2(50 BYTE),
  ACTIVITY_START        DATE,
  ACTIVITY_END          DATE,
  DIVISION              VARCHAR2(50 BYTE),
  ITEM_CODE             VARCHAR2(50 BYTE),
  MULT                  NUMBER,
  RETAIL                NUMBER,
  AD_PAGE               VARCHAR2(1 BYTE),
  FORECAST              NUMBER,
  MEMO                  VARCHAR2(50 BYTE)
INSERT INTO AD_LIST VALUES ('FILE_1','01-APR-2010','15-APR-2010','B',1111,5,10,'A',10,'This must be in my result');
INSERT INTO AD_LIST VALUES ('FILE_1','01-APR-2010','15-APR-2010','B',1111,1,1,'B',15,'Must not be in my result');
INSERT INTO AD_LIST VALUES ('FILE_1','01-APR-2010','15-APR-2010','B',1111,6,15,'C',11,'Must not be in my result');
INSERT INTO AD_LIST VALUES ('FILE_1','16-APR-2010','30-APR-2010','N',1111,4,20,'D',40,'Must not be in my result');
INSERT INTO AD_LIST VALUES ('FILE_1','16-APR-2010','30-APR-2010','N',1111,5,15,'E',30,'Must not be in my result');
INSERT INTO AD_LIST VALUES ('FILE_1','16-APR-2010','30-APR-2010','N',1111,1,2,'F',20,'This must be in my result');
CREATE TABLE PAGE_RANK
  AD_PAGE VARCHAR2(1 BYTE),
  RANK NUMBER
INSERT INTO PAGE_RANK VALUES ('A',1);
INSERT INTO PAGE_RANK VALUES ('B',2);
INSERT INTO PAGE_RANK VALUES ('C',3);
INSERT INTO PAGE_RANK VALUES ('D',4);
INSERT INTO PAGE_RANK VALUES ('E',5);
INSERT INTO PAGE_RANK VALUES ('F',6);
COMMIT;
SELECT * FROM AD_LIST
FILE     ACTIVITY     ACTIVITY          ITEM               AD
NAME     START          END          DIV     CODE     MULT     RETAIL     PAGE     FORECAST     MEMO
FILE_1     4/1/2010     4/15/2010     B     1111     5     10     A     10     This must be in my result
FILE_1     4/1/2010     4/15/2010     B     1111     1     1     B     15     Must not be in my result
FILE_1     4/1/2010     4/15/2010     B     1111     6     15     C     11     Must not be in my result
FILE_1     4/16/2010     4/30/2010     N     1111     4     20     D     40     Must not be in my result
FILE_1     4/16/2010     4/30/2010     N     1111     5     15     E     30     Must not be in my result
FILE_1     4/16/2010     4/30/2010     N     1111     1     2     F     20     This must be in my resultNow, from the table AD_LIST I want to group the records based on FILE_NAME, ACTIVITY_START, ACTIVITY_END, DIVISION, ITEM_CODE.
So in my example here we have 2 set of records grouped based on the columns specified.
Also we have one more table, PAGE_RANK, which has a rank corresponding to each ad_page number. Here 1 is higher rank than 2. Hence ad page 'A' takes priority over 'B'. Similarly for all other ad pages.
Now, we need to pick one ad from each group of ads by determining the highest ranked ad page within the group and the value for mult and retail must be replaced with the value that has min(retail/mult). So, using the above data we will have the one having ad page = 'A' and ad page = 'D' as the final results since they have highest ad page rank in their group.
The value for mult and retail values for ad_page 'A' = min (10/5 , 1/1, 15/6) = 1,1(mult,retail).
The value for mult and retail values for ad_page 'D' = min (20/4 , 15/5, 2/1) = 1,2(mult,retail).
Finally I have this query below
SELECT a.file_name,
       a.activity_start,
       a.activity_end,
       a.division,
       a.item_code,
       FIRST_VALUE (a.mult) OVER (PARTITION BY a.file_name, a.activity_start, a.activity_end, a.division, a.item_code ORDER BY (a.retail /
                                                                                                                                a.mult))
                                                                                                    mult,
       FIRST_VALUE (a.retail) OVER (PARTITION BY a.file_name, a.activity_start, a.activity_end, a.division, a.item_code ORDER BY (a.retail /
                                                                                                                                  a.mult))
                                                                                                  retail,
       FIRST_VALUE (a.ad_page) OVER (PARTITION BY a.file_name, a.activity_start, a.activity_end, a.division, a.item_code ORDER BY (b.RANK))
                                                                                                 ad_page,
       a.forecast,
       a.memo                                                                                                
  FROM ad_list a, page_rank b
WHERE a.ad_page = b.ad_pageThis query is giving me all the records but with the values what I wanted in Ad_Page, Mult and Retail columns.
How can I pick only one from each group.
I am getting this FILE     ACTIVITY     ACTIVITY          ITEM               AD
NAME     START          END          DIV     CODE     MULT     RETAIL     PAGE     FORECAST     MEMO
FILE_1     4/1/2010     4/15/2010     B     1111     1     1     A     15     Must not be in my result
FILE_1     4/1/2010     4/15/2010     B     1111     1     1     A     10     This must be in my result
FILE_1     4/1/2010     4/15/2010     B     1111     1     1     A     11     Must not be in my result
FILE_1     4/16/2010     4/30/2010     N     1111     1     2     D     20     This must be in my result
FILE_1     4/16/2010     4/30/2010     N     1111     1     2     D     30     Must not be in my result
FILE_1     4/16/2010     4/30/2010     N     1111     1     2     D     40     Must not be in my resultBut I want this FILE     ACTIVITY     ACTIVITY          ITEM               AD
NAME     START          END          DIV     CODE     MULT     RETAIL     PAGE     FORECAST     MEMO
FILE_1     4/1/2010     4/15/2010     B     1111     1     1     A     10     This must be in my result
FILE_1     4/16/2010     4/30/2010     N     1111     1     2     D     20     This must be in my resultI have to run this query for thousands of such group combination.
Hope some one can throw some light on this query.
Thanks in advance,
Raj.

Answer 1

Frank,
You are marvelous.
That is what I was expecting, but basically I want to display the row with highest page rank which is 'A' and 'D' in this case.
So I have changed my query as below using yours :
WITH mainq AS
     (SELECT a.file_name,
             a.activity_start,
             a.activity_end,
             a.division,
             a.item_code,
             FIRST_VALUE (a.mult) OVER (PARTITION BY a.file_name, a.activity_start, a.activity_end, a.division, a.item_code ORDER BY (a.retail /
                                                                                                                                      a.mult))
                                                                                                    mult,
             FIRST_VALUE (a.retail) OVER (PARTITION BY a.file_name, a.activity_start, a.activity_end, a.division, a.item_code ORDER BY (a.retail /
                                                                                                                                        a.mult))
                                                                                                  retail,
             --FIRST_VALUE (a.ad_page) OVER (PARTITION BY a.file_name, a.activity_start, a.activity_end, a.division, a.item_code ORDER BY (b.RANK))
             a.ad_page,
             a.forecast,
             a.memo,
             ROW_NUMBER () OVER (PARTITION BY a.file_name, a.activity_start, a.activity_end, a.division, a.item_code ORDER BY b.RANK)
                                                                                             AS r_num
        FROM ad_list a, page_rank b
       WHERE a.ad_page = b.ad_page)
SELECT *
  FROM mainq a
WHERE r_num = 1
FILE     ACTIVITY     ACTIVITY          ITEM               AD
NAME     START          END          DIV     CODE     MULT     RETAIL     PAGE     FORECAST     MEMO
FILE_1     4/1/2010     4/15/2010     B     1111     1     1     A     10     This must be in my result
FILE_1     4/16/2010     4/30/2010     N     1111     1     2     D     40     Must not be in my resultMy apologies that I gave you wrong forecast and memo values in my earlier post.
But that is what I wanted and your input greatly helped me to save lot of time by using in one single query.
Earlier I was using cursor to do that and it was not doing any good performance wise.
Thanks to every body for your time and your efforts.
I appreciate it.
Have fun.
~Raj