Oracle SQL: Joining another table with one missing tuple - sql

Question

I have the following two tables, one stores order information, one stores key|value information.
There is no CD = D for key COLOR_CD. I would like to join both tables to get all orders irregardless of the key|value pair not found in the MASS_DECODE table.
Can i get some help please :D
ORDER_INFORMATION
ORDER_NUMBER |COLOR_CD |
----------------|-----------|
1 |A |
2 |B |
3 |C |
4 |D |
MASS_DECODE
KEY |CD |VALUE |
------------|---------------|-----------|
COLOR_CD |A |Green |
COLOR_CD |B |Blue |
COLOR_CD |C |Red |
SIZE_CD |A |Large |
SIZE_CD |B |Medium |
SIZE_CD |C |Small |
SQL:
select order_number, cd, value
from order_information
left outer join mass_decode
on (color_cd = cd)
and key = 'COLOR_CD';
Outcome:
ORDER_NUMBER |CD |VALUE |
----------------|-----------|-----------|
1 |A |Green |
2 |B |Blue |
3 |C |Red |
Expected:
ORDER_NUMBER |CD |VALUE |
----------------|-----------|-----------|
1 |A |Green |
2 |B |Blue |
3 |C |Red |
4 |D |NULL |
EDIT: I am sorry i have presented incorrect information for my tables. Since been corrected.

Answer 1

select *
from order_information oi
left join mass_decode md
on (
oi.color_cd = md.cd
and oi.key = md.key
)
where oi.key = 'KEY_A';
SQLFiddle
upd:
According to your updates:
select *
from order_information oi
left join mass_decode md
on oi.color_cd = md.cd
where md.key = 'COLOR_CD' or md.key is null;
SQLFiddle

Answer 2

Your column names are ambiguous. You have two columns named the same in two tables, so which column does the key in your where clause refer to? I think in later versions of Oracle, this will actually give you an error. Try this:
select oi.order_number, oi.color_cd, md.value
from order_infomation oi
left outer join mass_decode md
on (oi.color_cd = md.cd)
where oi.key = 'KEY_A';
Edit:
Based on your response to #billy, it sounds like that wasn't working for you. You could also try putting the key predicate into the join clause:
select oi.order_number, oi.color_cd, md.value
from order_infomation oi
left outer join mass_decode md
on (oi.color_cd = md.cd) and oi.key = 'KEY_A';

Answer 3

This should do :
SELECT
order_number,
color_cd AS cd,
(
SELECT value FROM mass_decode m2 WHERE m2.key = o.key AND m2.cd = o.color_cd
) AS value
FROM order_information o
WHERE o.key = 'KEY_A'