Performance Issue using min() and max() in one SQL statement

Question

I have a simple query that selects min() and max() from one column in a table in one sql statment.
The table has about 9 Million rows and the selected column has a non unique index. The query takes 10 secs. When i select min() and max() in separate statements, each takes only 10 msecs:
This statement takes 10 secs:
select min(date_key) , max(date_key)
from CAPS_KPIC_BG_Fact_0_A
where date_key != TO_DATE(('1900-1-1' ),( 'YYYY-MM-DD'))
This statement takes 10 msecs:
select min(date_key)
from MYTABLE
where date_key != TO_DATE(('1900-1-1' ),( 'YYYY-MM-DD'))
union all
select max(date_key) from MYTABLE
Because the first statement is part of an autmatic generated SQL of an application, i can't change it and i have to optimize the data model. How can i speed up the first statement?

Answer 1

I've ran similar query on a table that has 10 milliion rows, with an index on the date column
This is what I have found:
SQL> set timing on
  1  SELECT MIN(ID_DATE) MIN_DATE, MAX(ID_DATE) MAX_DATE
  2      FROM MY_DATE
  3*     WHERE ID_DATE != TO_DATE(('1900-1-1' ),( 'YYYY-MM-DD'))
SQL> /
MIN_DATE  MAX_DATE
03-APR-76 06-JAN-02
real: 43383
SQL> SELECT MIN(ID_DATE) MIN_DATE FROM MY_DATE
  2   WHERE ID_DATE != TO_DATE(('1900-1-1' ),( 'YYYY-MM-DD'))
  3  UNION ALL
  4  SELECT MAX(ID_DATE) MAX_DATE FROM MY_DATE
  5   WHERE ID_DATE != TO_DATE(('1900-1-1' ),( 'YYYY-MM-DD'))
  6  /
MIN_DATE
03-APR-76
06-JAN-02
real: 20
SQL> SELECT MIN_DATE, MAX_DATE FROM
  2  (SELECT MAX(ID_DATE) MAX_DATE FROM MY_DATE
  3  WHERE ID_DATE != TO_DATE(('1900-1-1' ),( 'YYYY-MM-DD')) ) A,
  4  (SELECT MIN(ID_DATE) MIN_DATE FROM MY_DATE
  5  WHERE ID_DATE != TO_DATE(('1900-1-1' ),( 'YYYY-MM-DD')) ) B
  6  /
MIN_DATE  MAX_DATE
03-APR-76 06-JAN-02
real: 10
SQL> My conculsion, there is nothing you can do to the tables that will improve that particular statement.
Why can't you modify the application?