Aggregate functions across multiple columns in postgres

I have a postgresql table with multiple fields containing integers (a1,a2,a3 etc).

I want to run aggregate functions(mean, standard deviation etc) across more than one of the columns at once. (Some of them may have a reasonable number of nulls, so I don’t want to just generate column averages and then average those).

I can get a set of integers with

SELECT unnest(array[a1,a2,a3]) as values FROM table

but I then can’t get the aggregate functions to take this as input.

Can anyone give me any hints on how I could get this to work?

Answer

With a subquery you have all rows at your disposal:

SELECT sum(val) FROM (
    SELECT unnest(array[a1,a2,a3]) as val FROM table) alias;

You can also group your rows, for example:

SELECT field, sum(val) FROM (
    SELECT field, unnest(array[a1,a2,a3]) as val FROM table) alias
GROUP BY field;