unwrap postgresql array into rows

Question

What is the fastest way to unwrap array into rows in PostgreSQL? For instance,

We have:

a
-
{1,2}
{2,3,4}

And we need:

Answer 1

unnest --> expand an array to a set of rows

unnest(ARRAY[1,2]) 1 2

http://www.sqlfiddle.com/#!1/c774a/24