Interpreting cost on EXPLAIN PLAN

From: <artmt_at_hotmail.com>
Date: 16 Aug 2005 12:37:07 -0700
Message-ID: <1124221026.905778.9540@g47g2000cwa.googlegroups.com>

My understanding is that the cost value for "SELECT STATEMENT" at the top of the plan indicates what the optimizer estimates to be the total cost for the entire statement.

If this is true then how do I interpret plans that show low cost for "SELECT STATEMENT" and much larger cost for one of the operations?

In the example below "SELECT STATEMENT" cost=15 and "INDEX (RANGE SCAN)" cost=72.
I have also seen much bigger differences.

Thanks
-Art

   0 SELECT STATEMENT Optimizer=CHOOSE (Cost=15 Card=1 Bytes=111)    1 0 VIEW (Cost=15 Card=1 Bytes=111)

   2    1     WINDOW (SORT) (Cost=15 Card=1 Bytes=106)
   3    2       TABLE ACCESS (BY INDEX ROWID) OF 'RECEIPT' (Cost=2

Card=1 Bytes=76)

   4    3         NESTED LOOPS (Cost=13 Card=1 Bytes=106)
   5    4           VIEW (Cost=12 Card=1 Bytes=30)
   6    5             SORT (UNIQUE) (Cost=12 Card=1 Bytes=43)
   7    6               TABLE ACCESS (BY INDEX ROWID) OF 'RECEIPT'

(Cost=9 Card=1 Bytes=43)

   8    7                 INDEX (RANGE SCAN) OF 'RCTH_DT_DISTRIBUTE_I'
           (NON-UNIQUE) (Cost=72 Card=22)

   9    4           INLIST ITERATOR
  10    9             INDEX (RANGE SCAN) OF 'PK_RECEIPT' (UNIQUE)

(Cost=3 Card=1)
Received on Tue Aug 16 2005 - 14:37:07 CDT