Array extraction

Hi!

I have such table:

user_group
---------------------------------
ug_id -> serial primary key
ug_users -> int4[]

For example table has such rows:

 ug_id | ug_users

-------+--------------
  1    |  { 2,5,6 }
  2    |  { 3,4,9 }

I want to write SQL-query or write user defined function to get such result (extract array values):

 ug_id | ug_users
-------+--------------
  1    |    2
  1    |    5
 1    |    6
  2    |    3
  2    |    4
  2    |    9

Help please to solve this problem.

--
Vadim