Dynamic calculation formulas in Postgres

I'd like to know if there is a possibility to create something like named calculations in Postgres? Say, I have a table:

create table foo (
  bar smallint,
  baz smallint
)

I can run select (bar / baz) * 100 from foo; to get my result, but I'd like to have a formula (pseudocode): avg_foo ::= (bar/baz)*100 and then do select avg_foo from foo; to get the same result. Ideally, I'd like to have a separate table with calculations开发者_如何转开发:

create table calculations (
  name varchar,
  formula varchar
)

So that I could create calculations dynamically and use them in selects, like this:

insert into calculations (name, formula) values
  ('sum_bar_baz', 'bar+baz'),
  ('mult_bar_baz', 'bar*baz');
select sum_bar_baz, mult_bar_baz from foo;

How do I do this with Postgres?

Write a tuple returning function in plpgsql, and call the required functions from within.