Why can I not do a full outer join - sql

Question

I have a db2 query and I realized today I need to expand that query.
My table's already pretty complicated with joins, so I don't really want to add a union query. I want to do a full outer join.
At the moment, it's showing
SELECT
a.id
,a.city
,a.state
,case when a.thing = b.thing then a.thing else b.thing end
,sum( case when c.thing = 'thing' then 1 else 0 end)
,b.id
,b.name
FROM
a
INNER JOIN b -- I want to change this to FULL OUTER JOIN
ON a.id = b.id
LEFT JOIN c
ON a.id = c.id
LEFT JOIN (d
INNER JOIN e
ON d.id = e.id
)
WHERE
--logic
GROUP BY
--for the aggregate functions
ORDER BY
--logic
Can someone tell me when I try to do a full outer join, it says 'Full Outer Join is not supported for this query'? And how would I overcome that?
I think it's because of the other left joins.

Answer 1

It may not be able to combine the outer join with the left joins. You may have to make the outer join a subquery (also added some missing aliases and an ON clause):
SELECT
ab.a_id
,ab.city
,ab.state
,ab.thing
,sum( case when c.thing = 'thing' then 1 else 0 end)
,ab.b_id
,ab.name
FROM
(
SELECT
a.id a_id
,a.city
,a.state
,case when a.thing = b.thing then a.thing else b.thing end thing
,b.id b_id
,b.name
FROM
a
FULL OUTER JOIN b
ON a.id = b.id
) ab
LEFT JOIN c
ON ab.id = c.id
LEFT JOIN (d
INNER JOIN e
ON d.id = e.id
) f
ON ...
WHERE
--logic
GROUP BY
--for the aggregate functions
ORDER BY
--logic