Subquery conditional execution using cbo

Question

hellou
how i do for execute a subquery conditionally, using the cbo??
i got an example:
create table table1 AS
SELECT * FROM (
    SELECT 1 id, 'a' boss FROM dual
   union all
    SELECT 3 id, 'b' boss FROM dual
   union all
    SELECT 5 id, 'a' boss FROM dual
   union all
    SELECT 7 id, 'b' boss FROM dual
   union all
    SELECT 9 id, 'a' boss FROM dual
create index idx_table1 on table1(boss, id)
create table table2 AS
SELECT * FROM (
    SELECT 2 id, 'b' boss FROM dual
   union all
    SELECT 4 id, 'a' boss FROM dual
   union all
    SELECT 6 id, 'b' boss FROM dual
   union all
    SELECT 8 id, 'a' boss FROM dual
   union all
    SELECT 10 id, 'b' boss FROM dual
create index idx_table2 on table2(boss, id)
CREATE OR REPLACE FUNCTION print_hi
    isb in varchar2
return number
IS
BEGIN
    dbms_output.put_Line(isb);
    return 0;
END;
-- the query !!!!!!!
with data AS
    SELECT
    FROM (
        -- subquery #1
        SELECT
            1 query_name,
            id pibot,
            boss
        FROM table1
        WHERE print_hi(id) = 0
       union all
        -- subquery #2
        SELECT
            2 query_name,
            id pibot,
            boss
        FROM table2
SELECT
    pibot + query_name / 10 pibot
FROM data
WHERE 1 = 1
    AND boss = :boss
    AND (
        query_name = :q
        AND pibot > :p
       OR query_name > :q )
    AND rownum <= 3i want than only the query #2 be executed.
the query #1 print data in the screen when is executed (for the function print_hi).
now i execute the query with the variables data as:
boss = 'a'
q = 2
p = 0
when i execute the query using rules, then not print anything in the screen.
when i execute the query using costs, then print 1 5 9 in the screen. this means than the query #1 is being executed when this should not
help .. tx
SELECT * FROM v$version
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - Prod
PL/SQL Release 10.2.0.5.0 - Production
CORE10.2.0.5.0Production
TNS for Linux: Version 10.2.0.5.0 - Production
NLSRTL Version 10.2.0.5.0 - Production

Answer 1

As often is, the predicates section of the execution plan is quite revealing on this one.
Take your original query
explain plan for
with data AS
(SELECT *
FROM (-- subquery #1
       SELECT 1 query_name,id pibot,boss
       FROM table1
       WHERE print_hi(id) = 0
       union all
        -- subquery #2
       SELECT 2 query_name,id pibot,boss
        FROM table2))
SELECT pibot + query_name / 10 pibot
FROM   data
WHERE  1 = 1
AND    boss = :boss
AND   (query_name = :q
AND    pibot > :p
OR     query_name > :q )
AND    rownum <= 3;
select * from table(dbms_xplan.display);gives
| Id  | Operation           | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT    |            |     2 |    38 |     2   (0)| 00:00:01 |
|*  1 |  COUNT STOPKEY      |            |       |       |            |          |
|   2 |   VIEW              |            |     2 |    38 |     2   (0)| 00:00:01 |
|   3 |    UNION-ALL        |            |       |       |            |          |
|*  4 |     INDEX RANGE SCAN| IDX_TABLE1 |     1 |    16 |     1   (0)| 00:00:01 |
|*  5 |     INDEX RANGE SCAN| IDX_TABLE2 |     1 |    16 |     1   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - filter(ROWNUM<=3)
   4 - access("BOSS"=:BOSS)
       filter("PRINT_HI"(TO_CHAR("ID"))=0 AND (1>TO_NUMBER(:Q) OR
              1=TO_NUMBER(:Q) AND "ID">TO_NUMBER(:P)))
   5 - access("BOSS"=:BOSS)
       filter(2>TO_NUMBER(:Q) OR 2=TO_NUMBER(:Q) AND "ID">TO_NUMBER(:P))Assuming that the FILTER logic in STEP 4 is followed to order, it's not then possible with this query as is to short-circuit the evaluation of PRINT_HI as it is evaluated first.
When you make a change (just to q not necessarily to boss as well)
from
query_name = :qto
query_name = 2You'll hopefully notice the difference in predicate evaluation with the extra filter step:
| Id  | Operation             | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT      |            |     2 |    38 |     2   (0)| 00:00:01 |
|*  1 |  COUNT STOPKEY        |            |       |       |            |          |
|   2 |   VIEW                |            |     2 |    38 |     2   (0)| 00:00:01 |
|   3 |    VIEW               |            |     2 |    38 |     2   (0)| 00:00:01 |
|   4 |     UNION-ALL         |            |       |       |            |          |
|*  5 |      FILTER           |            |       |       |            |          |
|*  6 |       INDEX RANGE SCAN| IDX_TABLE1 |     1 |    16 |     1   (0)| 00:00:01 |
|*  7 |      INDEX RANGE SCAN | IDX_TABLE2 |     1 |    16 |     1   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - filter(ROWNUM<=3)
   5 - filter(1>TO_NUMBER(:Q))
   6 - access("BOSS"=:BOSS)
       filter("PRINT_HI"(TO_CHAR("ID"))=0)
   7 - access("BOSS"=:BOSS)
       filter("ID">TO_NUMBER(:P) OR 2>TO_NUMBER(:Q))