Only join two columns when it is not null in one table oracle - oracle

Question

I have a table a
ID | Name | City
1 |Jack | Null
2 |Tom | Null
And table b
ID | Name | City
1 |Jack | Dever
2 |Tom | Dallas
I need to write a query to join these two tables by id, name and city if they are not null in table a. But any of these three column could be null for each row.
I wrote one below but the performance is bad when data grows
Select * from a, b
Where (a.id is not null and a.id=b.id or a.id is null) and
(a.name is not null and a.name=b.name or a.name is null) and
(a.city is not null and a.city=b.city or a.city is null)
Basically, I need to join on the column when it is not null in table a.
Could you shed some light on this?
Thanks a lot!

Answer 1

ATTEMPT I:
Would this be what you need? It seems to do what I can read out from your question.
with a as (select 1 id, 'Jack' name, null city from dual
union all
select 2 id, 'Tom' name, null city from dual
union all
select 3 id, 'Mike' name, 'Miami' city from dual)
,b as (select 1 id, 'Jack' name, 'Dever' city from dual
union all
select 2 id, 'Tom' name, 'Dallas' city from dual
union all
select 3 id, 'Mike' name, 'Boise' city from dual)
select b.*
from b
left outer join a
on a.id = b.id
and a.name = b.name
where b.city = nvl(a.city, b.city);
If not, please advisa as to what would need to change in the result or possibly in the indata.
UPDATE I:
To allow all columns to have the possibility of being null, this could be one way of doing it. I've added testdata for the conditions I think your are describing. It gives the result I think you are looking for.
with a as (select 1 id, 'Jack' name, null city from dual
union all
select 2 id, 'Tom' name, null city from dual
union all
select 3 id, 'Mike' name, 'Miami' city from dual
union all
select 4 id, 'Don' name, null city from dual
union all
select 5 id, null name, 'London' city from dual
union all
select null id, 'Erin' name, 'Berlin' city from dual
)
,b as (select 1 id, 'Jack' name, 'Dever' city from dual
union all
select 2 id, 'Tom' name, 'Dallas' city from dual
union all
select 3 id, 'Mike' name, 'Boise' city from dual
union all
select 4 id, 'Don' name, 'Dover' city from dual
union all
select 5 id, 'Lis' name, 'London' city from dual
union all
select 6 id, 'Erin' name, 'Berlin' city from dual
)
select b.*, a.*
from b
inner join a
on b.id = nvl(a.id, b.id)
and b.name = nvl(a.name, b.name)
and b.city = nvl(a.city, b.city)
order by 1;