Query takes time to execute. Review this query and give me a possible quere

Question

SELECT DISTINCT A.REFERENCE_NUMBER
FROM A,B,C
WHERE DF_N_GET_CONTRACT_STATUS (A.REFERENCE_NUMBER, TRUNC (SYSDATE)) = 1
AND ( B.CHQ_RTN_INDICATOR IS NULL AND B.CHALLAN_NUMBER IS NULL
AND C.INSTRUMENT_TYPE IN (1, 2) AND C.MODULE_CODE = 5 )
AND ( A.HEADER_KEY = B.HEADER_KEY AND C.HEADER_KEY = B.HEADER_KEY);
This query takes 3 minutes to execute. I want to improve the performance so that it can execute with in seconds.
Table A has 10 lakhs record.
Table B has 3.7 lakhs record.
Table C has 5.3 lakhs record. Consider DF_N_GET_CONTRACT_STATUS as function. REFERENCE_NUMBER is the type of Varchar2(20).
Plz give me a correct logical and fastest execution query for the same.
Thanks in advance.

Answer 1

I would agree with the post from Santosh above that you should review the guidelines for posting a tuning request. This is VERY important. It is impossile to come up with any useful suggestions without the proper information.
In the case of your query, I would probably focus my attention on the function that you have defined. What happens if the condition using the DF_N_GET_CONTRACT_STATUS function is removed? Does it still take 3 minutes?
SELECT reference_number
from (
  SELECT DISTINCT A.REFERENCE_NUMBER
  FROM A,B,C
  WHERE ( B.CHQ_RTN_INDICATOR IS NULL AND B.CHALLAN_NUMBER IS NULL
  AND C.INSTRUMENT_TYPE IN (1, 2) AND C.MODULE_CODE = 5 )
  AND ( A.HEADER_KEY = B.HEADER_KEY AND C.HEADER_KEY = B.HEADER_KEY)
where DF_N_GET_CONTRACT_STATUS(reference_number, trunc(sysdate)) = 1;Of course, the query above really depends on the cardinality of the returned data..... which is impossible to know without following the posting guidelines. This query could return anywhere between 0 rows and 2x10^17 rows. And in the latter case evaluating the function at the end wouldn't make any difference.
Also, do you really need the distinct? Does it make any difference? Most of the time that I see distinct, to me it either means the query is wrong or the data model is wrong.