explain plan for select participantgroup
from    sourceprocresult outer
                   where  participantgroup <> ' '
                   AND sprid IN
                   (select max(sprid)
                    from   sourceprocresult inner
                    where   spuid = 100000000
                    and     sprid < 1521);

---------------------------------------------------------------------------------------------------
| Id  | Operation                      | Name             | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |                  |     1 |    10 |     8   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS BY INDEX ROWID   | SOURCEPROCRESULT |     1 |    10 |     4   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN             | SPR_SPRID        |     1 |       |     3   (0)| 00:00:01 |
|   3 |    SORT AGGREGATE              |                  |     1 |    14 |            |          |
|*  4 |     TABLE ACCESS BY INDEX ROWID| SOURCEPROCRESULT |     1 |    14 |     4   (0)| 00:00:01 |
|*  5 |      INDEX RANGE SCAN          | SPR_SPRID        |     1 |       |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------------




 explain plan for select /*+ CARDINALITY(outer 1)*/ participantgroup
 from    sourceprocresult outer
                    where  participantgroup <> ' '
                    AND sprid IN
                    (select max(sprid)
                     from   sourceprocresult inner
                     where   spuid = 100000000
                     and     sprid < 1521)
/

---------------------------------------------------------------------------------------------------
| Id  | Operation                      | Name             | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |                  |     1 |    10 |     8   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS BY INDEX ROWID   | SOURCEPROCRESULT |     1 |    10 |     4   (0)| 00:00:01 |
|*  2 |   INDEX RANGE SCAN             | SPR_SPRID        |     1 |       |     3   (0)| 00:00:01 |
|   3 |    SORT AGGREGATE              |                  |     1 |    14 |            |          |
|*  4 |     TABLE ACCESS BY INDEX ROWID| SOURCEPROCRESULT |     1 |    14 |     4   (0)| 00:00:01 |
|*  5 |      INDEX RANGE SCAN          | SPR_SPRID        |     1 |       |     3   (0)| 00:00:01 |
---------------------------------------------------------------------------------------------------