Cursor(s) in procedure

Question

Hi!
In a procedure there are 2 select statements that have to be handled separately because of 2 different conditions:
1. condition:
IF route_id and segment_id IS NULL THEN ...1.statement - selects non-stop flights:
CURSOR c1 IS
SELECT carrier_code, flight_no, from_city, origin, dept_time, to_city, destination, arr_time, flight_date,
aircraft_type, booking_class, service_class, num_of_seats, checked_bag, fare_basis, fare_type, currency, rt_net_fare, tax, surcharges, fare_total
FROM favailability
WHERE (from_city = p_city_o
        AND to_city = p_city_d
        AND service_class = p_service_class
        AND fare_type = p_fare_type
        AND flight_date = p_flightdate)
OR    (from_city = p_city_d
        AND to_city = p_city_o
        AND service_class = p_service_class
        AND fare_type = p_fare_type_rt
        AND flight_date = p_flightdate_rt)
ORDER BY flight_date;2. condition:
ELSE route_id and segment_id IS NOT NULL THEN ...2.statement - select 1-stop flights
CURSOR c1 IS
SELECT *
FROM
        SELECT FLIGHT_LEG_ID
        ,       ROUTE_ID
        ,       SEGMENT_ID
        ,       CARRIER_CODE
        ,       FLIGHT_NO
        ,       FROM_CITY
        ,       ORIGIN
        ,       DEPT_TIME
        ,       TO_CITY
        ,       DESTINATION
        ,       ARR_TIME
        ,       FLIGHT_DATE
        ,       ACTUAL_ARRIVAL_DATE
        ,       AIRCRAFT_TYPE
        ,       BOOKING_CLASS
        ,       SERVICE_CLASS
        ,       NUM_OF_SEATS
        ,       CHECKED_BAG
        ,       FARE_BASIS
        ,       FARE_TYPE
        ,       CURRENCY
        ,       RT_NET_FARE
        ,       TAX
        ,       SURCHARGES
        ,       FARE_TOTAL
        ,       MIN(ORIGIN) KEEP (DENSE_RANK FIRST ORDER BY SEGMENT_ID) OVER (PARTITION BY ROUTE_ID) AS ORG
        ,       MIN(DESTINATION) KEEP (DENSE_RANK LAST ORDER BY SEGMENT_ID) OVER (PARTITION BY ROUTE_ID) AS DST
        FROM favailability
WHERE route_id IS NOT NULL
AND segment_id IS NOT NULL
WHERE (from_city = p_city_o or to_city = p_city_d)
        AND service_class = p_service_class
        AND fare_type = p_fare_type
        AND flight_date = p_flightdate
OR
       (from_city = p_city_d or to_city = p_city_o)
        AND service_class = p_service_class
        AND fare_type = p_fare_type_rt
        AND flight_date = p_flightdate_rt
order by flight_date;My questions are:
1) How to place this in a procedure, FOR, LOOP ...
2) Are 2 cursors necessary or can 1 cursor handle both selects?

Answer 1

Hi there!
1) When you mention FOR...LOOP I'm going to "assume" you mean the following construct:
FOR each_rec IN (<Your cursor SELECT statement here>) LOOP
  .....code
  .....code
END LOOP;..to loop through the contents of the returned data set and perform operations, checks etc.
2)Your select statements differ in the number of columns returned so that would neccessitate two separate cursors as you have now.
If the fields returned were the SAME you could "potentially" use certain techniques that can selectively execute WHERE clauses based on other variables etc. (as seen at this link: Re: adding dynamic where/and condition to the cursor - however, this may cause unwanted side effects like indexes not being used if present.
As it stands, I would keep the code as it is - it's logically easier to see what is exactly happening and the processing "overhead" of two separate cursros will be absolutely negligible!
HTH - Chris
....Afterthought.....
If you want to place this process into one select statement you could use UNION ALL and erffectively place the PL/SQL IF statements into the WHERE clause in the following manner:
SELECT <fields in FIRST statement>
FROM <table>
WHERE
           (route_id IS NULL and segment_id IS NULL) -- This statement controls if the first part of the SELECT statement is executed
AND
...<Rest of WHERE clause in FIRST statement>
UNION ALL
SELECT <fields in SECOND statement>
FROM <table>
WHERE
           (route_id IS NOT NULL and segment_id IS NOT NULL) -- This statement controls if the second part of the SELECT statement is executed
AND
...<Rest of WHERE clause in SECOND statement>This should also keep indexes available for use in the optimiser plan!
Edited by: FFS on 30-Oct-2009 13:32