create table t1 (id char(4),c1 char(4))

create table t2 (id char(4),c1 char(4))

insert into t1 values (1,null)

insert into t2 values (1,null)

insert into t1 values (2,9)

insert into t2 values (2,9)

insert into t1 values (3,null)

insert into t2 values (3,8)

insert into t1 values (4,'+')

insert into t2 values (4,'+')

insert into t1 values (5,'*')

insert into t2 values (5,'!')

insert into t1 values (6,'a')

insert into t2 values (6,null)

insert into t1 values (7,'b')

insert into t2 values (7,'b')

insert into t1 values (8,'c')

insert into t2 values (8,'d')

Compare Columns

select  
  t1.id,  
  t1.c1 "one", 
  t2.c1 "two", 
  case 
  when t1.c1= t2.c1 then 'EQ'
  when t1.c1 is null and t2.c1 is null then 'EQ'
  end "a" 
from  
  t1, t2 
 where t1.id=t2.id