Having trouble in a PL/SQL program - plsql

Question

I have a table(pay_period) as following
pay_period
period_id list_id start_date end_date price
1 100 2017-01-01 2017-08-31 100
2 100 2017-09-01 2017-12-31 110
3 101 2017-01-01 2017-08-31 75
Now I have list_id, checkin_date, checkout_date
list_id 100
checkin_date 2017-08-25
checkout_date 2017-09-10
I need to calculate the price of a list for the period from checkin date to checkout date.
therefore the calculation is supposed to be
7 * 100 + 10 * 110
I am thinking to do it with a for loop, if there is any other better way to do it, can you please suggest?

Answer 1

You have to see if the checkin_date and checkout_date are into the same period_id.
1.1 If yes, you multiply the price with the nunmber of days.
1.2 If no, you have count the days between checkin_day untill the end of your period 1 and multiply with the corresponding price, then do the same with checkout_day and beginning of next period.
Note: i guess it might happen to have more than 2 prices per list_id. for example:
period_id list_id start_date end_date price
1 100 2017-01-01 2017-04-30 100
2 100 2017-05-01 2017-09-30 110
3 100 2017-10-01 2017-12-31 120
4 101 2017-01-01 2017-08-31 75
and the calculation period to be:
list_id 100
checkin_date 2017-03-01
checkout_date 2017-11-10
In this case, yes, the solution would be to have a CURSOR where to keep the prices for list_id and periods; loop through it and compare the checkin_date and checkout_date with each record.
Best,
Mikcutu.

Answer 2

You can do the following for a much cleaner code. Although it is purely sql, I am using a function to make it code better to understand.
Create a generic function which gets you the number of overlapping days in 2 different date range.
CREATE OR REPLACE FUNCTION fn_count_range
( p_start_date1 IN DATE,
p_end_date1 IN DATE,
p_start_date2 IN DATE,
p_end_date2 IN DATE ) RETURN NUMBER AS
v_days NUMBER;
BEGIN
IF p_end_date1 < p_start_date1 OR p_end_date2 < p_start_date2 THEN
RETURN 0;
END IF;
SELECT COUNT(*) INTO v_days
FROM (
(SELECT p_start_date1 + LEVEL - 1
FROM dual CONNECT BY LEVEL <= p_end_date1 - p_start_date1 + 1 ) INTERSECT
(SELECT p_start_date2 + LEVEL - 1
FROM dual CONNECT BY LEVEL <= p_end_date2 - p_start_date2 + 1 ) );
RETURN v_days;
END;
/
Now, your query to calculate the total price is simplified.
WITH lists ( list_id,
checkin_date,
checkout_date) AS
( SELECT 100,
TO_DATE('2017-08-25','YYYY-MM-DD'),
TO_DATE('2017-09-10','YYYY-MM-DD')
FROM dual) --Not required if you have a lists table.
SELECT l.list_id,
SUM(fn_count_range(start_date,end_date,checkin_date,checkout_date) * price) total_price
FROM pay_period p
JOIN lists l ON p.list_id = l.list_id
GROUP BY l.list_id;