Unexpected Tkprof Row Count

Oracle 8.1.7.2.1 EE on HP-UX 11

Does anyone know of a reason why a SORT (GROUP BY) row source operation would increase the number of rows returned from a query...

I thought that a GROUP BY would reduce the number of rows, not increase them...

Here is the TKPROF output which shows that a JOIN between 2 tables ('PS_TM_PEFF_GPQCAL' and 'PS_TM_PEFF_BNCHMRK') returns about 110,000 rows but when this is passed up to the GROUP BY operation, the row count jumps up to 7.3 million.

Rows Execution Plan

-------  ---------------------------------------------------
      0  SELECT STATEMENT   GOAL: CHOOSE
     61   SORT (ORDER BY)
     61    VIEW
   1464     WINDOW (SORT)
   1464      SORT (GROUP BY)
   1464       HASH JOIN (OUTER)
   1464        HASH JOIN
   1464         VIEW OF 'PS_TM_PEFF_V_SHDAY'
   1464          SORT (UNIQUE)
   1464           UNION-ALL
   1176            FILTER
   1177             NESTED LOOPS
   1177              NESTED LOOPS (OUTER)
   1177               HASH JOIN
     42                MERGE JOIN (CARTESIAN)
      2                 NESTED LOOPS
      2                  INDEX   GOAL: ANALYZED (UNIQUE 
                             SCAN) OF 'PS_TM_PEFF_SHPMSTR' (UNIQUE)
      2                  TABLE ACCESS   GOAL: ANALYZED 
                             (FULL) OF 'PS_TM_PEFF_TCJR'
     42                 SORT (JOIN)
     42                  TABLE ACCESS   GOAL: ANALYZED 
                             (FULL) OF 'PS_TM_PEFF_T_CONTR'
   6220                TABLE ACCESS   GOAL: ANALYZED (FULL) 
                           OF 'PS_TM_PEFF_TWTCAL'
   1176               TABLE ACCESS   GOAL: ANALYZED (FULL) OF 
                          'PS_TM_PEFF_COEF'
   2352              VIEW OF 'PS_TM_PEFF_V_CCEH'
7314720               SORT (GROUP BY)
 110312                FILTER
 145807                 NESTED LOOPS (OUTER)
 110465                  TABLE ACCESS   GOAL: ANALYZED (BY 
                             INDEX ROWID) OF 'PS_TM_PEFF_GPQCAL'
 114449                   INDEX   GOAL: ANALYZED (RANGE 
                              SCAN) OF 'PS_TM_PEFF_GPQCAL' (UNIQUE)
 136124                  TABLE ACCESS   GOAL: ANALYZED (BY 
                             INDEX ROWID) OF 'PS_TM_PEFF_BNCHMRK'
 246588                   INDEX (RANGE SCAN) OF 
                              'PSATM_PEFF_BNCHMRK' (UNIQUE)
    138             SORT (AGGREGATE)
     69              TABLE ACCESS   GOAL: ANALYZED (FULL) OF 


                         'PS_TM_PEFF_TCJR'

   1556             SORT (AGGREGATE)
    868              INDEX   GOAL: ANALYZED (FAST FULL SCAN) OF 


                         'PS_TM_PEFF_T_CONTR' (UNIQUE)

     96             SORT (AGGREGATE)
     48              FIRST ROW
     48               INDEX   GOAL: ANALYZED (RANGE SCAN 
                          (MIN/MAX)) OF 'PS_TM_PEFF_COEF' (UNIQUE)
    288            NESTED LOOPS
     43             MERGE JOIN (CARTESIAN)
      2              TABLE ACCESS   GOAL: ANALYZED (FULL) OF 


                         'PS_TM_PEFF_TCJR'

     43              SORT (JOIN)
     42               TABLE ACCESS   GOAL: ANALYZED (FULL) OF 
                          'PS_TM_PEFF_T_CONTR'
    288             TABLE ACCESS   GOAL: ANALYZED (BY INDEX 
                        ROWID) OF 'PS_TM_PEFF_TWTCAL'
   1650              INDEX   GOAL: ANALYZED (RANGE SCAN) OF 


                         'PS_TM_PEFF_TWTCAL' (UNIQUE)

   1536               SORT (AGGREGATE)
   1824                INDEX   GOAL: ANALYZED (RANGE SCAN) OF 
                           'PS_TM_PEFF_CONTRIB' (UNIQUE)
    110               SORT (AGGREGATE)
     55                TABLE ACCESS   GOAL: ANALYZED (FULL) 
                           OF 'PS_TM_PEFF_TCJR'
     24         VIEW OF 'PS_TM_PEFF_V_MFCAL'
   1095          WINDOW (SORT)
   1095           TABLE ACCESS   GOAL: ANALYZED (FULL) OF 
                      'PS_TM_PEFF_MFCAL'
   2248        VIEW OF 'PS_TM_PEFF_V_TGTCC'
   2248         HASH JOIN (OUTER)
    476          TABLE ACCESS   GOAL: ANALYZED (FULL) OF 
                     'PS_CMS_DPTDPTS'
   7248          INDEX   GOAL: ANALYZED (FAST FULL SCAN) OF 
                     'PS_TM_PEFF_TRGT_CC' (UNIQUE)