I am using filter() to return a filtered range of cells. Of that result, I only want one column of the results (so that I can sum the values of that column). What is the syntax (or function) that I can use to do that?

I want to sum the values in column D that correspond to rows with "key_match" in column C. 

I want to do something like: =SUM(GET_COLUMN(FILTER(B:F, C:C = "key_match"), D:D)). Filter rows of columns B-F where cells in column C == "key_match"; of that result, I want to calculate the sum of the values in column D. How can do what I would like GET_COLUMN() to do?