Why outer join query not working? - sql

Question

Hallo,
my objective is to generate a table that shows the total of each CODE that belong to the owner, take note that each owner must have a CODE tied to it no matter the TOTAL value is zero. So there will be APP, REJ, CAN tied to each of the APPROVAL_ID.
APPROVAL_ID CODE TOTAL
----------- ---- -----
101 APP 2
101 REJ 1
101 CAN 3
102 APP 2
102 REJ 4
102 CAN 0
103 APP 0
103 REJ 0
103 CAN 4
Thus, here is the source code:
select approval_id, code, total
from (
select 'APP' code, '1' seq from dual
union all
select 'REJ' code, '2' seq from dual
union all
select 'CAN' code, '3' seq from dual
)
left outer join (
select m.approval_id, own.name, m.decision, count(*) total,
case own.channel
when 'CH1' then 'CH1'
when 'CH2' then 'CH2'
else 'Others Channel'
end the_channel
from tableM m, owner own
where m.decision in ('REJ', 'APP', 'CAN')
and own.id=m.approval_id
group by m.approval_id, own.name, m.decision, own.channel
order by m.approval_id
)
on code=decision
group by approval_id, code, total
order by approval_id;
The output from the above query is like below:
APPROVAL_ID CODE TOTAL
----------- ---- -----
101 APP 2
101 REJ 1
101 CAN 3
102 APP 2
102 REJ 4
103 CAN 4
The output of the inner query is like below:
APPROVAL_ID CODE TOTAL
----------- ---- -----
101 APP 2
101 REJ 1
101 CAN 3
102 APP 2
102 REJ 4
103 CAN 4
Something was not right to the query because I know that some of the row is having total value of zero, it should print something like (null) value in it. But why does it hidden from the view? Is there anything wrong to my query?
THanks #!

Answer 1

First, you need to do a cross join between your owner and your code table.
Then you do the left join.
I have modelised 3 table : Type for your 3 lines APP, REJ and CAN, then a user table, equivalent to your owner table, and a third table decision, equivalent to your tableM.
The query looks like this :
SELECT c.user_id, c.type_code, COUNT(d.id)
FROM
(
SELECT t.ID as type_id, u.id as user_id, t.CODE as type_code
FROM Type t, Userr u
) c
LEFT OUTER JOIN Decision d
ON d.user_id = c.user_id
AND d.type_id = c.type_id
GROUP BY c.user_id, c.type_code
Not tested but for yours set of table :
select a.id_own, a.code, count(m.approval_id)
from
(
select code, own.id as id_own
from (
select 'APP' code, '1' seq from dual
union all
select 'REJ' code, '2' seq from dual
union all
select 'CAN' code, '3' seq from dual
) , owner own
) a
left outer join tableM m
on a.code = m.decision
and a.id_own = m.approval_id
group by a.id_own, a.code
order by a.id_own
Note that the count(m.approval_id) will give you the number of approval_id that appear not null in the left join.

Answer 2

Your outer join is on code=decision. That means you get one row for each codes which don't occur as decision on the right side. Obviously you want to do your left join with a cross join of 3 codes and all distinct APPROVAL_IDs giving all the combinations of code and APPROVAL_ID on the left side.

Answer 3

My first guess is that
group by approval_id, code, total
should be
group by approval_id, code