Confusion in FILTER and SORT operations in the execution plan

Question

Hi
I have been working on tuning of a sql query:
SELECT SUM(DECODE(CR_FLG, 'C', NVL(TOT_AMT, 0), 0)),
       SUM(DECODE(CR_FLG, 'C', 1, 0)),
       SUM(DECODE(CR_FLG, 'R', NVL(TOT_AMT, 0), 0)),
       SUM(DECODE(CR_FLG, 'R', 1, 0)),
       SUM(DECODE(CR_FLG, 'C', NVL(TOT_AMT, 0), -1 * NVL(TOT_AMT, 0))),
       SUM(1)
     FROM TS_TEST
    WHERE SMY_DT BETWEEN TO_DATE(:1, 'DD-MM-YYYY') AND
       TO_DATE(:1, 'DD-MM-YYYY');Table TS_TEST is range partitioned on smy_dt and there is an index on smy_dt column. Explain plan of the query is:
SQL> explain plan for  SELECT SUM(DECODE(CR_FLG, 'C', NVL(TOT_AMT, 0), 0)),
  2         SUM(DECODE(CR_FLG, 'C', 1, 0)),
  3         SUM(DECODE(CR_FLG, 'R', NVL(TOT_AMT, 0), 0)),
  4         SUM(DECODE(CR_FLG, 'R', 1, 0)),
  5         SUM(DECODE(CR_FLG, 'C', NVL(TOT_AMT, 0), -1 * NVL(TOT_AMT, 0))),
  6         SUM(1)
  7    FROM TS_TEST
  8   WHERE SMY_DT BETWEEN TO_DATE(:1, 'DD-MM-YYYY') AND
  9         TO_DATE(:1, 'DD-MM-YYYY');
Explained.
SQL> @E
PLAN_TABLE_OUTPUT
Plan hash value: 766961720
| Id  | Operation                            | Name                | Rows  | Bytes | Cost (%CPU)| Time     | Pstart| Pstop |
|   0 | SELECT STATEMENT                     |                     |     1 |    14 | 15614   (1)| 00:03:08 |       |       |
|   1 |  SORT AGGREGATE                      |                     |     1 |    14 |            |             |       |       |
|*  2 |   FILTER                             |                     |       |       |            |          |       |       |
|   3 |    TABLE ACCESS BY GLOBAL INDEX ROWID| T_TEST             | 79772 |  1090K| 15614   (1)| 00:03:08 | ROWID | ROWID |
|*  4 |     INDEX RANGE SCAN                 | I_SMY_DT         |   143K|       |   442   (1)| 00:00:06 |       |       |
Predicate Information (identified by operation id):
   2 - filter(TO_DATE(:1,'DD-MM-YYYY')<=TO_DATE(:1,'DD-MM-YYYY'))
   4 - access("SMY_DT">=TO_DATE(:1,'DD-MM-YYYY') AND "SMY_DT"<=TO_DATE(:1,'DD-MM-YYYY'))
17 rows selected.
SQL>I am not able to understand the FILTER & SORT operations. As there is an index on SMY_DT column, so index range scan is fine. But why a FILTER (Step no 2) and SORT (Step no 1) operation after that ?
Oracle version is 10.2.0.3 on AIX 5.3 64 bit.
Any other information required please let me know.
Regards,
Amardeep Sidhu

Answer 1

Sort aggregate tells you that there was performed an aggregate operation which returns one row, in opposite to sort order by or hash group by which indicates you have grouping, and there more than one row can be returned.
SQL> SELECT SUM(comm) FROM emp;
SUM(COMM)
      2200
Plan wykonywania
Plan hash value: 2083865914
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT   |      |     1 |     2 |     3   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE    |      |     1 |     2 |            |          |
|   2 |   TABLE ACCESS FULL| EMP  |    14 |    28 |     3   (0)| 00:00:01 |
SQL> SELECT AVG(comm) FROM emp;
AVG(COMM)
       550
Plan wykonywania
Plan hash value: 2083865914
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT   |      |     1 |     2 |     3   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE    |      |     1 |     2 |            |          |
|   2 |   TABLE ACCESS FULL| EMP  |    14 |    28 |     3   (0)| 00:00:01 |
SQL> SELECT MIN(comm) FROM emp;
MIN(COMM)
         0
Plan wykonywania
Plan hash value: 2083865914
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT   |      |     1 |     2 |     3   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE    |      |     1 |     2 |            |          |
|   2 |   TABLE ACCESS FULL| EMP  |    14 |    28 |     3   (0)| 00:00:01 |
SQL> SELECT deptno, SUM(comm) FROM emp GROUP BY deptno;
    DEPTNO  SUM(COMM)
        30       2200
        20
        10
Plan wykonywania
Plan hash value: 4067220884
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT   |      |     3 |    15 |     4  (25)| 00:00:01 |
|   1 |  HASH GROUP BY     |      |     3 |    15 |     4  (25)| 00:00:01 |
|   2 |   TABLE ACCESS FULL| EMP  |    14 |    70 |     3   (0)| 00:00:01 |
SQL>Edited by: Łukasz Mastalerz on Jan 14, 2009 11:41 AM