Counting payment from date range in MySQL - php

Question

I want to count payment within selected date, but i can't figure it out how to do it.
Here is the example data from the my table
id starts_from payment_per_day
=======================================
1 2012-01-01 10,000.00
2 2012-01-15 10,500.00
3 2012-02-01 11,000.00
4 2012-02-15 11,500.00
5 2012-03-01 12,000.00
How do i count total payment from 2012-01-21 to 2012-02-20 ?
The total payment should be 338,500
from 2012-01-21 to 2012-01-31 = 11 days * 10,500
from 2012-02-01 to 2012-02-14 = 14 days * 11,000
from 2012-02-15 to 2012-02-20 = 6 days * 11,500
But if i do :
SELECT SUM(payment_per_day) as total FROM table
WHERE starts_from BETWEEN '2012-01-21' AND '2012-02-20'
the result is only 22,500
Any ideas ?

Answer 1

SELECT SUM(payment_per_day) as total FROM table
WHERE starts_from BETWEEN '2012-01-21' AND '2012-02-20';

Answer 2

I would first expand the range into the list of dates, then use the following query:
SELECT SUM(p1.payment_per_day)
FROM dates d
INNER JOIN payments p1 ON p1.starts_from <= d.date
LEFT JOIN payments p2 ON p2.starts_from <= d.date
AND p2.starts_from > p1.starts_from
WHERE p2.id IS NULL
You could obtain the list from the range with the help of a numbers table, like this:
SELECT DATE_ADD(#date_from, INTERVAL num DAY)
FROM numbers
WHERE num BETWEEN 0 AND DATEDIFF(#date_to, #date_from)
A numbers table is a thing worth having as it can be useful in many situations, so consider providing yourself with one. Here's a very simple script to create and initialise a numbers table:
CREATE TABLE numbers AS SELECT 0 AS num;
SET #ofs = (SELECT COUNT(*) FROM numbers); INSERT INTO numbers SELECT #ofs + num FROM numbers;
SET #ofs = (SELECT COUNT(*) FROM numbers); INSERT INTO numbers SELECT #ofs + num FROM numbers;
SET #ofs = (SELECT COUNT(*) FROM numbers); INSERT INTO numbers SELECT #ofs + num FROM numbers;
… /* repeat as necessary, each line doubles the number of rows in the table */
But, of course, you can use a loop instead.
Here's my complete testing environment on SQL Fiddle (for anyone to play with).

Answer 3

It seems that it is almost impossible to do query like that, counting total each day payment within selected date.
So i work around by selecting data from all starts_from dates until <= 2012-02-20 and then picking last starts_from date which is less than 2012-01-21 (that is 2012-01-15) in order to get payment_per_day 10,500.00
Thank you for viewing my question :)