CPU Cost of a Query without executing it?

Question

Is there any mathematical formula to find CPU cost of a query without executing it? Thanks

Answer 1

902181 wrote:
Is there any mathematical formula to find CPU cost of a query without executing it? ThanksAny why do you want the cost? What do you expect it to tell you? How are you planning to apply this in your code? Make sure you understand what cost tells you and what it does not tell you. And use that value in a sane fashion.
As for an alternative to using EXPLAIN PLAN, you can simply parse a SQL into a cursor without executing it. Then determine the SQL cursor id and address and use DBMS_XPLAN to display its execution plan.
E.g.
SQL> create or replace procedure ParseSQL( sqlStatement varchar2 ) is
  2          c       integer;
  3  begin
  4          c := DBMS_SQL.open_cursor;
  5 
  6          DBMS_SQL.parse(
  7                  c,
  8                  sqlStatement,
  9                  DBMS_SQL.native
10          );
11 
12          DBMS_SQL.close_cursor( c );
13  end;
14  /
Procedure created.
SQL>
SQL> var sqlID varchar2(100)
SQL> var childNumber number
SQL> var sqlText varchar2(4000)
SQL> begin
  2          ParseSQL( 'select /* TEST1 */  * from emp' );
  3 
  4          select
  5                  sql_text, sql_id, child_number into :sqlText, :sqlID, :childNumber
  6          from    v$sql
  7          where   sql_text like 'select /* TEST1 */%';
  8  end;
  9  /
PL/SQL procedure successfully completed.
SQL>
SQL> col PLAN_TABLE_OUTPUT format a50
SQL> select
  2          rownum, p.plan_table_output
  3  from       TABLE( DBMS_XPLAN.Display_Cursor( :sqlID, :childNumber, 'BASIC,COST' ) ) p;
    ROWNUM PLAN_TABLE_OUTPUT
         1 EXPLAINED SQL STATEMENT:
         2 ------------------------
         3 select /* TEST1 */  * from emp
         4
         5 Plan hash value: 3956160932
         6
         7 -----------------------------------------------
         8 | Id  | Operation         | Name | Cost (%CPU)|
         9 -----------------------------------------------
        10 |   0 | SELECT STATEMENT  |      |     3 (100)|
        11 |   1 |  TABLE ACCESS FULL| EMP  |     3   (0)|
        12 -----------------------------------------------
        13
13 rows selected.
SQL> The problem is extracting intelligence from the output as it is raw text. Perhaps not that complex as a where clause can be added to only display line id 0 and then extract the cost value from that line. Regular expressions (not my forte) will likely do this easily.