Weighted Mean extension for PostgreSQL
This extension provides a "weighted mean" aggregate function for postgreql.
The weighted mean is defined as a two columns aggregation function, one containing the measure to be averaged, the second containing the weight of each measure.
This extensions is implemented as a C library.
You can either install it with the pgxn client:
pgxn install weighted_mean
Or from source:
git clone git://github.com/Kozea/weighted_mean.git make && sudo make install
Then, create the extension in the specific database:
CREATE extension weighted_mean;
select weighted_mean(unitprice, quantity) from sales;
This is equivalent to:
select case when sum(quantity) = 0 then 0 else sum(unitprice * quantity) / sum(quantity) end from sales;