select COL1 from MY_TABLE
UNION
select COL2 from MY_TABLE

create table my_table as
select 'адрес1' col1,	'адрес2' col2 from dual union all
select 'адрес3' col1,	'адрес4' col2 from dual union all
select 'адрес2' col1,	'адрес5' col2 from dual union all
select 'адрес6' col1,	'адрес3' col2 from dual;


select DISTINCT GROUP_CONCAT(DISTINCT c ORDER BY c)
from 
  (
    select 
      if(t.a=1, @a:=@a+1, @a) n,
      case t.a 
        when 1 then t1.col1
        when 2 then t1.col2
        when 3 then t2.col1
        when 4 then t2.col2
      end c
    from
    (
      select @a:=0
    ) tt,
    (
      select 1 a union all
      select 2 a union all
      select 3 a union all
      select 4 a
    ) t,
    my_table t1
    INNER  JOIN my_table t2
      on (t1.col1 in (t2.col1, t2.col2) or t1.col2 in (t2.col1, t2.col2)) 
          and (t1.col1 != t2.col1 and t1.col2 != t2.col2)
  ) res
GROUP BY n