How to tune this select

Question

Hi all,
Can anyone suggests me how to speed up the following query? What index should I create?
The Query
SELECT *
FROM SCHEDULE_EMP
WHERE EMP_NO = :b2
AND :b1 BETWEEN START_DATE AND END_DATE
Table Structure
EMP_NO NOT NULL VARCHAR2(10)
START_DATE NOT NULL DATE
END_DATE DATE
SAT NUMBER(2)
SUN NUMBER(2)
MON NUMBER(2)
TUE NUMBER(2)
WED NUMBER(2)
THU NUMBER(2)
FRI NUMBER(2)
Thanks in advance.

Answer 1

Hello
It really helps with this kind of task if you can post the execution plan, and also list what existing indexes you have on the table, volumes of data etc.
In this case though, with the limited information I would suggest creating an index on emp_no and start_date. Is there a reason why end_date doesn't have a not null constraint? If nulls are valid in end_date, I would have thought you could need to modify the where clause to take that into account. Unfortunately I don't have a database to test on at the mo but I would think you would need to do something like:
SELECT
FROM
     SCHEDULE_EMP
WHERE
     EMP_NO = :b2
AND
     start_date <= :b1
AND
     end_date >= :b1
AND
     end_date IS NOT NULL
...or this one if you want to consider nulls in end_date.....
SELECT
FROM
     SCHEDULE_EMP
WHERE
     EMP_NO = :b2
AND
               start_date <= :b1
          AND
               end_date >= :b1
          AND
               end_date IS NOT NULL
     OR
               start_date <= :b1
          AND
               end_date IS NULL
     )If you only want to consider rows with a value in end_date, including it in the index may well prove to be a good move but you would need to try it out.
HTH
David