Oracle convert DECODE to PIVOT or force use of index - oracle

Question

I have a very complex SQL view definition that has been inherited and requires altering to improve performance. It takes a list of records based on a foreign key and displays the rows returned as columns.
Thus :-
Data from select using RANK
ID RANK DKEY RECORD1 RECORD2 RECORD3
1 1 1 003 Rob Emmerry
1 2 2 004 Sue Emmerry
Returns
ID REC11 REC12 REC13 REC21 REC22 REC23
1 003 Rob Emmerry 004 Sue Emmerry
There are 37 columns of data repeated for each returned row upto a max of 5.
Using
SELECT ID,
MIN(DECODE(ranking,1,RECORD1, NULL)) AS REC11
MIN(DECODE(ranking,1,RECORD2, NULL)) AS REC12
MIN(DECODE(ranking,1,RECORD3, NULL)) AS REC13
MIN(DECODE(ranking,1,RECORD4, NULL)) AS REC14
MIN(DECODE(ranking,1,RECORD5, NULL)) AS REC15
MIN(DECODE(ranking,1,RECORD6, NULL)) AS REC16
MIN(DECODE(ranking,2,RECORD1, NULL)) AS REC21
MIN(DECODE(ranking,2,RECORD2, NULL)) AS REC22
MIN(DECODE(ranking,2,RECORD3, NULL)) AS REC23
MIN(DECODE(ranking,2,RECORD4, NULL)) AS REC24
MIN(DECODE(ranking,2,RECORD5, NULL)) AS REC25
MIN(DECODE(ranking,2,RECORD6, NULL)) AS REC26
FROM
(
SELECT ID, RANK () OVER (PARTITION BY id ORDER BY dkey) ranking,
RECORD1,
RECORD2,
RECORD3,
RECORD4,
RECORD5,
RECORD6
FROM TABLEA
JOIN
(SELECT ID, DKEY, RECORD4, RECORD5, RECORD6
FROM TABLEB
) ON TABLEB.DKEY = TABLEA.DKEY AND TABLEB.ID = TABLEA.ID
)
GROUP BY ID;
When using the explain plan and filtering on the DKEY field which has an index the index is ignored presumably because of the min/decode statements.
So I thought about rewriting this using PIVOT but don't know how to start.
Any thoughts as to how I can
a) Get the query to use the index
b) Rewrite using PIVOT
First option is obviously preferable.
Thanks
Craig
UPDATE
Here is some sample data showing how my tables are.
Table 1
DKEY PID RECORD1 RECORD2 RECORD3
1 1 3 Rob Emmerry
2 1 4 Sue Emmerry
3 1 4 Jan Morris
4 1 4 Sue Pye
5 1 4 Jane Taylor
Table 2
CID DKEY RECORD10
1 3 A
2 3 D
3 3 G
4 3 J
5 4 A
6 5 A
7 5 D
8 6 A
9 6 D
10 6 G
11 7 A
12 7 D
13 7 G
14 7 J
15 7 M
Table 3
QID DKEY RECORD3
1 3 C
2 6 C
3 6 F
4 7 C
5 7 F
So tables 2 & 3 link to table 1 with DKEY
If we took the DKEY=3 as an example I would want to see this:-
PID DKEY REC1 REC2 REC3 REC4 REC5 REC6 REC7 REC8 REC9 REC10 REC11 REC12 REC13
1 3 4 Jan Morris A D G J NULL C NULL NULL NULL NULL
There could be up to 5 rows in each of tables 2 & 3. Fields PID, DKEY, REC1-REC3 from table 1, REC4-REC8 come from table 2 and the rest from table 3. The other records from table 1 would simply continue on the row so after REC13, DKEY=4 etc etc.
Hope this makes sense.

Answer 1

SELECT
ID,
MIN(DECODE(ranking,1,RECORD1, NULL)) AS REC11,
MIN(DECODE(ranking,1,RECORD2, NULL)) AS REC12,
MIN(DECODE(ranking,1,RECORD3, NULL)) AS REC13,
MIN(DECODE(ranking,1,RECORD4, NULL)) AS REC14,
MIN(DECODE(ranking,1,RECORD5, NULL)) AS REC15,
MIN(DECODE(ranking,1,RECORD6, NULL)) AS REC16,
MIN(DECODE(ranking,2,RECORD1, NULL)) AS REC21,
MIN(DECODE(ranking,2,RECORD2, NULL)) AS REC22,
MIN(DECODE(ranking,2,RECORD3, NULL)) AS REC23,
MIN(DECODE(ranking,2,RECORD4, NULL)) AS REC24,
MIN(DECODE(ranking,2,RECORD5, NULL)) AS REC25,
MIN(DECODE(ranking,2,RECORD6, NULL)) AS REC26
FROM
(
SELECT /*+ INDEX(tablea tablea_index) */
ID,
RANK () OVER (PARTITION BY id ORDER BY dkey) ranking,
RECORD1,
RECORD2,
RECORD3,
RECORD4,
RECORD5,
RECORD6
FROM TABLEA
JOIN TABLEB
-- was: ON TABB.DKEY = TABLEA.DKEY AND TABB ON TABB.ID = TABLEA.ID
ON TABLEB.DKEY = TABLEA.DKEY
AND TABLEB.ID = TABLEA.ID
)
GROUP BY ID;