Question

Col 1,
col 2,
.....
.....
from 
table1,
table2
........
........
where
join conditions1
join conditions1
................
.................
and
table1.day_key >= (select key from date_dim where value='01-JAN-2011')
and table1.day_key <= (select key from date_dim where value='31-DEC-2011')
and 
table2.day_key >= (select key from date_dim where value='01-JAN-2011')
and table2.day_key <= (select key from date_dim where value='31-DEC-2011')

Here I can see date_dim table is doing scan four in where condition, how to avoid it. date_dim table is not selected in main from clause. I dont have enviornment to test this unfortunatly. Database is oracle 10g

Answer 1

As I said I don’t see a performance problem scanning that table double times as necessary.

A pure rewrite of query would be:

select 
  Col 1,
  col 2,
from 
  table1,
  table2,
  date_dim date_dim_start,
  date_dim date_dim_end
where
  join conditions1
  join conditions1 and
  table1.day_key >=  date_dim_start.key and
  table1.day_key <= date_dim_end.key and
  table2.day_key >= date_dim_start.key and
  table2.day_key <= date_dim_end.key and
  date_dim_start.value = '01-JAN-2011' and
  date_dim_end.value='31-DEC-2011';

But you should test it, in order to not suffer a performance hit.