create or replace function random_string(integer)
returns text as
$body$
select array_to_string(array(select substring(‘0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz‘ FROM (ceil(random()*62))::int FOR 1) FROM generate_series(1, $1)), ‘‘);
$body$
language sql volatile;
原文：http://www.cnblogs.com/strinkbug/p/5141047.html