E-Rows = NULL and A-Rows=42M? Need help in understanding why.

Question

Hi,
Oracle Standard Edition 11.2.0.3.0 CPU Oct 2012 running on Windows 2008 R2 x64. I am using Oracle 10g syntax for WITH clause as the query will also run on Oracle 10gR2. I do not have a Oracle 10gR2 environment at hand to comment if this behaves the same.
Following query is beyond me. It takes around 2 minutes to return the "computed" result set of 66 rows.
SQL> WITH dat AS
  2          (SELECT 723677 vid,
  3                  243668 fid,
  4                  TO_DATE ('06.03.2013', 'dd.mm.yyyy') mindt,
  5                  TO_DATE ('06.03.2013', 'dd.mm.yyyy') maxdt
  6             FROM DUAL
  7           UNION ALL
  8           SELECT 721850,
  9                  243668,
10                  TO_DATE ('06.02.2013', 'dd.mm.yyyy'),
11                  TO_DATE (' 22.03.2013', 'dd.mm.yyyy')
12             FROM DUAL
13           UNION ALL
14           SELECT 723738,
15                  243668,
16                  TO_DATE ('16.03.2013', 'dd.mm.yyyy'),
17                  TO_DATE ('  04.04.2013', 'dd.mm.yyyy')
18             FROM DUAL)
19      SELECT /*+ GATHER_PLAN_STATISTICS */ DISTINCT vid, fid, mindt - 1 + LEVEL dtshow
20        FROM dat
21  CONNECT BY LEVEL <= maxdt - mindt + 1
22  order by fid, vid, dtshow;
66 rows selected.
SQL>
SQL> SELECT * FROM TABLE (DBMS_XPLAN.display_cursor (NULL, NULL, 'ALLSTATS LAST'));
PLAN_TABLE_OUTPUT
SQL_ID  9c4vma4mds6zk, child number 0
WITH dat AS         (SELECT 723677 vid,                 243668 fid,
            TO_DATE ('06.03.2013', 'dd.mm.yyyy') mindt,
TO_DATE ('06.03.2013', 'dd.mm.yyyy') maxdt            FROM DUAL
UNION ALL          SELECT 721850,                 243668,
   TO_DATE ('06.02.2013', 'dd.mm.yyyy'),                 TO_DATE ('
22.03.2013', 'dd.mm.yyyy')            FROM DUAL          UNION ALL
    SELECT 723738,                 243668,                 TO_DATE
('16.03.2013', 'dd.mm.yyyy'),                 TO_DATE ('  04.04.2013',
'dd.mm.yyyy')            FROM DUAL)     SELECT /*+
GATHER_PLAN_STATISTICS */ DISTINCT vid, fid, mindt - 1 + LEVEL dtshow
    FROM dat CONNECT BY LEVEL <= maxdt - mindt + 1 order by fid, vid,
dtshow
Plan hash value: 1865145249
| Id  | Operation                              | Name | Starts | E-Rows | A-Rows |   A-Time   |  OMem |  1Mem | Used-Mem |
|   0 | SELECT STATEMENT                       |      |      1 |        |     66 |00:01:54.64 |       |       |          |
|   1 |  SORT UNIQUE                           |      |      1 |      3 |     66 |00:01:54.64 |  6144 |  6144 | 6144  (0)|
|   2 |   CONNECT BY WITHOUT FILTERING (UNIQUE)|      |      1 |        |     42M|00:01:04.00 |       |       |          |
|   3 |    VIEW                                |      |      1 |      3 |      3 |00:00:00.01 |       |       |          |
|   4 |     UNION-ALL                          |      |      1 |        |      3 |00:00:00.01 |       |       |          |
|   5 |      FAST DUAL                         |      |      1 |      1 |      1 |00:00:00.01 |       |       |          |
|   6 |      FAST DUAL                         |      |      1 |      1 |      1 |00:00:00.01 |       |       |          |
|   7 |      FAST DUAL                         |      |      1 |      1 |      1 |00:00:00.01 |       |       |          |
--------------------------------------------------------------------------------------------------------------------------If I take out one of the UNION queries, the query returns in under 1 second.
SQL> WITH dat AS
  2          (SELECT 723677 vid,
  3                  243668 fid,
  4                  TO_DATE ('06.03.2013', 'dd.mm.yyyy') mindt,
  5                  TO_DATE ('06.03.2013', 'dd.mm.yyyy') maxdt
  6             FROM DUAL
  7           UNION ALL
  8           SELECT 721850,
  9                  243668,
10                  TO_DATE ('06.02.2013', 'dd.mm.yyyy'),
11                  TO_DATE (' 22.03.2013', 'dd.mm.yyyy')
12             FROM DUAL)
13      SELECT /*+ GATHER_PLAN_STATISTICS */ DISTINCT vid, fid, mindt - 1 + LEVEL dtshow
14        FROM dat
15  CONNECT BY LEVEL <= maxdt - mindt + 1
16  order by fid, vid, dtshow;
46 rows selected.
SQL>
SQL> SELECT * FROM TABLE (DBMS_XPLAN.display_cursor (NULL, NULL, 'ALLSTATS LAST'));
PLAN_TABLE_OUTPUT
SQL_ID  1d2f62uy0521p, child number 0
WITH dat AS         (SELECT 723677 vid,                 243668 fid,
            TO_DATE ('06.03.2013', 'dd.mm.yyyy') mindt,
TO_DATE ('06.03.2013', 'dd.mm.yyyy') maxdt            FROM DUAL
UNION ALL          SELECT 721850,                 243668,
   TO_DATE ('06.02.2013', 'dd.mm.yyyy'),                 TO_DATE ('
22.03.2013', 'dd.mm.yyyy')            FROM DUAL)     SELECT /*+
GATHER_PLAN_STATISTICS */ DISTINCT vid, fid, mindt - 1 + LEVEL dtshow
    FROM dat CONNECT BY LEVEL <= maxdt - mindt + 1 order by fid, vid,
dtshow
Plan hash value: 2232696677
| Id  | Operation                              | Name | Starts | E-Rows | A-Rows |   A-Time   |  OMem |  1Mem | Used-Mem |
|   0 | SELECT STATEMENT                       |      |      1 |        |     46 |00:00:00.01 |       |       |          |
|   1 |  SORT UNIQUE                           |      |      1 |      2 |     46 |00:00:00.01 |  4096 |  4096 | 4096  (0)|
|   2 |   CONNECT BY WITHOUT FILTERING (UNIQUE)|      |      1 |        |     90 |00:00:00.01 |       |       |          |
|   3 |    VIEW                                |      |      1 |      2 |      2 |00:00:00.01 |       |       |          |
|   4 |     UNION-ALL                          |      |      1 |        |      2 |00:00:00.01 |       |       |          |
|   5 |      FAST DUAL                         |      |      1 |      1 |      1 |00:00:00.01 |       |       |          |
|   6 |      FAST DUAL                         |      |      1 |      1 |      1 |00:00:00.01 |       |       |          |
26 rows selected.What I cannot understand is why the E-Rows is NULL for "CONNECT BY WITHOUT FILTERING (UNIQUE)" step and A-Rows shoots up to 42M for first case. The behaviour is the same for any number of UNION queries above two.
Can anyone please help me understand this and aid in tuning this accordingly? Also, I would be happy to know if there are better ways to generate the missing date range.
Regards,
Satish

Answer 1

May be, this?
WITH dat AS
            (SELECT 723677 vid,
                    243668 fid,
                    TO_DATE ('06.03.2013', 'dd.mm.yyyy') mindt,
                    TO_DATE ('06.03.2013', 'dd.mm.yyyy') maxdt
               FROM DUAL
             UNION ALL
             SELECT 721850,
                    243668,
                   TO_DATE ('06.02.2013', 'dd.mm.yyyy'),
                   TO_DATE (' 22.03.2013', 'dd.mm.yyyy')
              FROM DUAL
            UNION ALL
            SELECT 723738,
                   243668,
                   TO_DATE ('16.03.2013', 'dd.mm.yyyy'),
                   TO_DATE ('  04.04.2013', 'dd.mm.yyyy')
              FROM DUAL)
       SELECT  vid, fid, mindt - 1 + LEVEL dtshow
         FROM dat
  CONNECT BY LEVEL <= maxdt - mindt + 1
      and prior vid = vid
      and prior fid = fid
      and prior sys_guid() is not null
  order by fid, vid, dtshow;
66 rows selected.
Elapsed: 00:00:00.03