Question

I have a query which is crossing two tables

select count(*) from ingenium.empevt, ingenium.evt where empevt_evtfk = evt_pk

it takes quite a long time to run and in trying to figure out why I looked at the plan

    Operation   Object Name Rows    Bytes   Cost    Object Node In/Out  PStart  PStop

SELECT STATEMENT Optimizer Mode=CHOOSE      634 K       75981                                
  HASH JOIN     634 K   180 M   75981                                
    HASH JOIN       845 K   234 M   8930                                 
      HASH JOIN     465 K   53 M    3118                                 
        NESTED LOOPS        620 K   15 M    1618                                 
          NESTED LOOPS      1   20      2                                
            TABLE ACCESS BY INDEX ROWID INGENIUM.USR    1   10      1                                
              INDEX UNIQUE SCAN INGENIUM.XAK1USR    1                                        
            TABLE ACCESS BY INDEX ROWID INGENIUM.USR    1   10      1                                
              INDEX UNIQUE SCAN INGENIUM.XAK1USR    1                                        
          INDEX RANGE SCAN  INGENIUM.SECUSREMP_USREMP   89 M    600 M   1616                                 
        TABLE ACCESS FULL   INGENIUM.TBLEMP 620 K   55 M    1150                                 
      TABLE ACCESS FULL INGENIUM.TBLEMPEVT  1 M 182 M   4000                                 
    TABLE ACCESS FULL   INGENIUM.SECUSREMP  89 M    600 M   27013 

What I don’t like is the table access full on INGENIUM.SECUSREMP_USREMP which has a huge number of rows. I don’t know why it is scanning that table since it wasn’t in the query. INGENIUM.SECUSREMP_USREMP has a foreign key which references into ingenium.emp.emp_pk, however I don’t see why that would matter.

Is there some way to rewrite this query such that it doesn’t scan a seemingly unrelated table? Why is it scanning that table in the first place?

Answer 1

Presumably both empevt and evt are views, not tables? Your query plan shows (only) these tables being accessed:

• USR
• TBLEMP
• TBLEMPEVT
• SECUSREMP

What are the definitions of these views? Unless of course you are looking at the wrong plan!