Index not used in a simple query

Question

Hi all,
I have a query which is using only 2 tables linked with an indexed column, i'm surprised that the 2 tables are not using index and they are full scanned. here is some details:
Table a: T1 (col11 number, col12 varchar2) indexed on col11 (primary key): rows number=4 millions indexe: idx1 on col11
Table b: T2 (col21 number, col22 varchar2) indexed on col21 (primary key): rows number=3 millions indexe: idx2 on col21
select a.col12, b.col22 from T1 a, T2 b where a.col11=b.col21
The execution plan is:
Operation     Object Name     Rows     Bytes     Cost     Object Node     In/Out     PStart     PStop
SELECT STATEMENT Optimizer Mode=ALL_ROWS          3 M           32356                                          
  PX COORDINATOR                                                                
    PX SEND QC (RANDOM)     SYS.:TQ10002     3 M     67 M     32356       :Q1002      P->S       QC (RANDOM)      
      HASH JOIN          3 M     67 M     32356       :Q1002      PCWP                        
        PX RECEIVE          3 M     20 M     7376       :Q1002      PCWP                        
          PX SEND HASH     SYS.:TQ10001     3 M     20 M     7376       :Q1001      P->P       HASH             
            PX BLOCK ITERATOR          3 M     20 M     7376       :Q1001      PCWC                        
              TABLE ACCESS FULL     T2     3 M     20 M     7376       :Q1001      PCWP                        
        BUFFER SORT                             :Q1002      PCWC                        
          PX RECEIVE          3 M     44 M     24708       :Q1002      PCWP                        
            PX SEND HASH     SYS.:TQ10000     3 M     44 M     24708              S->P       HASH             
              TABLE ACCESS FULL     T1     3 M     44 M     24708                                           Thanks

Answer 1

Hi Herald,
Thanks for your reply
when selecting only the columns which are indexed, it is using the index
select a.account_link_code_n, b.account_link_code_n from gsm_sims_master a, gsm_service_mast b
where a.account_link_code_n=b.account_link_code_n
See the execution below:
Operation     Object Name     Rows     Bytes     Cost     Object Node     In/Out     PStart     PStop
SELECT STATEMENT Optimizer Mode=ALL_ROWS          3 M           11051                                          
  PX COORDINATOR                                                                
    PX SEND QC (RANDOM)     SYS.:TQ10002     3 M     44 M     11051       :Q1002      P->S       QC (RANDOM)      
      HASH JOIN          3 M     44 M     11051       :Q1002      PCWP                        
        PX RECEIVE          3 M     20 M     7376       :Q1002      PCWP                        
          PX SEND HASH     SYS.:TQ10001     3 M     20 M     7376       :Q1001      P->P       HASH             
            PX BLOCK ITERATOR          3 M     20 M     7376       :Q1001      PCWC                        
              TABLE ACCESS FULL     GSM_SERVICE_MAST     3 M     20 M     7376       :Q1001      PCWP                        
        BUFFER SORT                             :Q1002      PCWC                        
          PX RECEIVE          3 M     22 M     3403       :Q1002      PCWP                        
            PX SEND HASH     SYS.:TQ10000     3 M     22 M     3403              S->P       HASH             
              INDEX FAST FULL SCAN     ABILLITY.SIM_ACC_LNK_CD_IDX     3 M     22 M     3403                                                     But using hints has a very bad execution plan and a very high cost:
select /*+ index(a) index(b) */ a.account_link_code_n, b.account_link_code_n from gsm_sims_master a, gsm_service_mast b
where a.account_link_code_n=b.account_link_code_n
Operation     Object Name     Rows     Bytes     Cost     Object Node     In/Out     PStart     PStop
SELECT STATEMENT Optimizer Mode=ALL_ROWS          3 M           31899                                          
  HASH JOIN          3 M     44 M     31899                                          
    INDEX FULL SCAN     ABILLITY.GSM_SERV_MAST#ACLINK_CODE$PK     3 M     20 M     8158                                          
    INDEX FULL SCAN     ABILLITY.SIM_ACC_LNK_CD_IDX     3 M     22 M     15709                                           Thank you
Luc