Merging Records with same or NULL values

Question

Hi,
create table AS_ITM (id_itm NUMBER, diff_1 VARCHAR2(20), diff_2 VARCHAR2(20));
insert into as_itm values (22188212, 'J068', 'C001');
select id_itm, diff_1, diff_2 from as_itm;
output:
22188212     J068     C001
create table RK_DIFF_DESC (diff_id VARCHAR2(20), diff_type VARCHAR2(20), diff_desc VARCHAR2(20));
insert into RK_DIFF_DESC values ('C001', 'C', 'Red');
insert into RK_DIFF_DESC values ('J068', 'S', '6.8gm');
select diff_id, diff_type, diff_desc from RK_DIFF_DESC;
output:
C001 C     Red
J068     S     6.8gm
Now I am writting a query to get the out put ::
SELECT i.id_itm,
i.dept_id,
CASE WHEN (DIFF.DIFF_TYPE = 'S') THEN diff.DIFF_DESC ELSE NULL END
AS SIZE1,
CASE WHEN (DIFF.DIFF_TYPE = 'C') THEN diff.DIFF_DESC ELSE NULL END
AS COLOR
FROM as_itm i
LEFT OUTER JOIN
RK_DIFF_DESC diff
ON (i.diff_1 = diff.DIFF_ID OR i.diff_2 = diff.DIFF_ID);
output:
ID_ITM     DEPT_ID     SIZE1     COLOR
22188212     4103      6.8gm     
22188212     4103          Red
My requirement is to get a single record like this:
ID_ITM     DEPT_ID     SIZE1     COLOR
22188212     4103      6.8gm     Red
I can do this joining RK_DIFF_DESC two times with AS_ITM using below query.
SELECT a.id_itm,
a.dept_id,
b.diff_desc size1,
c.diff_desc COLOR
FROM as_itm a
LEFT OUTER JOIN RK_DIFF_DESC b
ON (a.diff_1 = b.DIFF_ID AND b.diff_type = 'S')
LEFT OUTER JOIN RK_DIFF_DESC c
ON (a.diff_2 = c.DIFF_ID AND c.diff_type = 'C')
Is there any other way to merge the above two lines into one joining RK_DIFF_DESC only 1 time ?
..............................

Answer 1

select id_itm, max(SIZE1) SIZE1,  max(COLOR) COLOR
from
select id_itm,
        case diff_type when 'S' then diff_desc end SIZE1,
        case diff_type when 'C' then diff_desc end COLOR
from AS_ITM a, RK_DIFF_DESC r
where diff_1 = diff_id or diff_2 = diff_id
group by id_itm;
    ID_ITM SIZE1                COLOR              
  22188212 6.8gm                Red                
1 row selected.