unwrap postgresql array into rows

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:

b
- 
1
2
2
3
4

I'm using:

select explode_array(a) as a from a_table;

where explode_array is:

create or replace function explode_array(in_array anyarray) returns setof anyelement as
$$
    select ($1)[s] from generate_series(1,array_upper($1, 1)) as s;
$$

Is there any better way?

Use unnest. For example:

CREATE OR REPLACE FUNCTION test( p_test text[] )
  RETURNS void AS
$BODY$
BEGIN
  SELECT id FROM unnest( p_test ) AS id;
END;
$BODY$
  LANGUAGE plpgsql IMMUTABLE
  COST 1;

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

unnest(ARRAY[1,2])
1
2

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

If you have a table users_to_articles like:

user_id	articles
1	{1,2}
2	{6,2,7}

And need to explode the articles array so to obtain:

user_id	article_id
1	1
1	2
2	6
2	2
2	7

You could run something like that:

CREATE TABLE "users_to_articles" (
  "user_id" SERIAL PRIMARY KEY,
  "articles" INT[]
);

INSERT INTO "users_to_articles" ("articles")
VALUES ('{1,2}'), ('{6,2,7}');

SELECT
  "user_id"
, "article_id"
FROM "users_to_articles", unnest("articles") AS "article_id";

Here is a working sqlfiddle:
http://www.sqlfiddle.com/#!17/c26742/1