Calculating the Weighted Average Cost of products stock

Question

I have to calculate my products stock cost, so for every product after each buy, i have to recalculate the Weighted Average Cost.

I got a view thats

Answer 1

I have spent several hours on this moving average! Mainly because of the not reliable window function first/last/nth_value, according to Postgresql documentation on window functions: This is likely to give unhelpful results for nth_value and particularly last_value.

The answer is incomplete. Things to do:

• make WAC stay the same value when qty_in = 0 (now it is zeroed out)
• WAC is not calculated based on previous WAC but on "previous" price, that's why there are increasing differences between WAC calculated by me and presented by You

SQLFiddle