Update a cell based on two matching fields in separate tabs within a range

Question

I'm trying to update a cell in Google Spreadsheets where its value comes from another sheet and based on the date range entered with it.

Here is what the two worksheets look like in the file.

Debtor Payments Sheet

January
Name | Amount Recieved | Date Recieved
Joe     $2.00            1/20/2011  
Kim     $1.00            1/25/2011                   


November
Name | Amount Recieved | Date Recieved
Joe     $6.00            2/11/2011  

Debtor Payment By Month Sheet

Name | Jan   | Feb
Joe    $2.00   $6.00
Kim    $1.00

What I want to happen is:

1. When a payment is made in a given month in "Debtor Payments Sheet".
2. Add the amount to "Debtor Payment By Month Sheet" in the column for that month where the name matches.

With these conditions:

• the name will only show up once in Pay by Month
• New names will be added to "Debtor Payments" and need to be put manually or otherwise into "Debtor Payment By Month Sheet"

Answer 1

Basically, you need to use a few formulas to accomplish this, like:

UNIQUE
FILTER
SUM

Walk through the spreadsheet I prepared and see the formula's for yourself: file I prepared with example