Extract all tags from hstore field
You are looking for the skeys function:

select skeys(hstore_column)
from the_table;


If you also need the values for each key:

select (a).key, (a).value
from (
  select each(hstore_column) as a
  from the_table
) t;


More details in the manual: http://www.postgresql.org/docs/current/static/hstore.html