Tuning Query with IN-Operator

Question

Hi all,
I have to tune the statement below.
UPDATE TABLE_A A
SET A.FIELD1 =
(SELECT B.FIELD1 FROM TABLE_B B WHERE B.IDENTNO IN (A.IDENTNO, A.IDENTNO||'000')
There are indexes on identno on TABLE_A and TABLE_A
The subquery returns only one row. The query works, but not fast enough.
I tried to split the where condition to join it together again with a union like this
UPDATE TABLE_A A
SET A.FIELD1 =
(SELECT B.FIELD1 FROM TABLE_B B WHERE B.IDENTNO = A.IDENTNO
UNION
SELECT B.FIELD1 FROM TABLE_B B WHERE B.IDENTNO = A.IDENTNO||'000')
But the execution plan shows a full table scan for the second part of the union.
How can I tune this part ? With function based index ?
Thanks in advance.
Henning

Answer 1

Please see this thread
When your query takes too long ...
You need to make sure if your statistics are up to date. If not analyze the table.
It works for me,
SQL*Plus: Release 9.2.0.6.0 - Production on Tue May 31 17:10:38 2011
Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.8.0 - 64bit Production
With the Partitioning, Oracle Label Security, OLAP and Oracle Data Mining options
JServer Release 9.2.0.8.0 - Production
SQL> CREATE TABLE TABLE_A AS SELECT 1 field1,'1000' IDENTNO FROM dual;
Table created.
SQL> CREATE TABLE TABLE_B AS SELECT 1 field1,'1000000' IDENTNO FROM dual;
Table created.
SQL> CREATE INDEX idx13 ON table_B(IDENTNO);
Index created.
SQL> CREATE INDEX idx12 ON table_A(IDENTNO);
Index created.
SQL> set autotrace on
SQL> UPDATE TABLE_A A
  2     SET A.FIELD1 =
  3            (SELECT B.FIELD1
  4               FROM TABLE_B B
  5              WHERE B.IDENTNO IN (A.IDENTNO, A.IDENTNO || '000'));
1 row updated.
Execution Plan
   0      UPDATE STATEMENT Optimizer=CHOOSE
   1    0   UPDATE OF 'TABLE_A'
   2    1     TABLE ACCESS (FULL) OF 'TABLE_A'
   3    1     CONCATENATION
   4    3       TABLE ACCESS (BY INDEX ROWID) OF 'TABLE_B'
   5    4         INDEX (RANGE SCAN) OF 'IDX13' (NON-UNIQUE)
   6    3       TABLE ACCESS (BY INDEX ROWID) OF 'TABLE_B'
   7    6         INDEX (RANGE SCAN) OF 'IDX13' (NON-UNIQUE)
Statistics
          2  recursive calls
          2  db block gets
          8  consistent gets
          0  physical reads
        424  redo size
        353  bytes sent via SQL*Net to client
        432  bytes received via SQL*Net from client
          3  SQL*Net roundtrips to/from client
          2  sorts (memory)
          0  sorts (disk)
          1  rows processed
SQL>