Help me in date comparision Please !!! urgent.

Question

Hi ,
I am trying to retrieve some entries from a table for a selected date.
Here is the quest I am running .
SELECT C.idnumber,A.fullname, A.description FROM Contact C, Action A WHERE TO_CHAR(c_date,'mm/dd/yyyy')='02/16/2009' AND C.actioncode = A.code ;
This statement is correct . But the abouve query is not using the index which defined on c_date as it is enclosed with TO_CHAR .
Can any one tell me how can I alter the above query such that it use the index & gives me data for a user selected date.
Please share if you have any ideas & help me out to sort the issue.
-Meena

Answer 1

A DATE column does not have a format-- it is stored in the same packed binary format. Date format masks are only important when you go to convert a date to a string for display.
If you want to ignore the time component of the date, you would need to TRUNC your date, i.e.
SELECT C.idnumber,A.fullname, A.description
  FROM Contact C,
       Action A
WHERE TRUNC(c_date) = to_date('02/16/2009', 'mm/dd/yyyy')
   AND C.actioncode = A.code ;Of course, this will prevent Oracle from using an index on C_DATE. The solution to this is to create a function-based index on TRUNC( c_date ), i.e.
CREATE INDEX idx_trunc_cdate
  ON contact ( TRUNC( c_date ) );Oracle would then be able to use the new index IDX_TRUNC_CDATE for your query. If all your queries want to ignore the time component, you may want to evaluate whether you can get rid of the index on C_DATE alone.
Justin