When or why would you use a right outer join instead of left?

Question

Wikipedia states:

\"In practice, explicit right outer joins are rarely used, since they can always be replaced with left outer joins and provide no additional functi

Answer 1

I've never used right join before and never thought I could actually need it, and it seems a bit unnatural. But after I thought about it, it could be really useful in the situation, when you need to outer join one table with intersection of many tables, so you have tables like this:

And want to get result like this:

Or, in SQL (MS SQL Server):

declare @temp_a table (id int)
declare @temp_b table (id int)
declare @temp_c table (id int)
declare @temp_d table (id int)

insert into @temp_a
select 1 union all
select 2 union all
select 3 union all
select 4

insert into @temp_b
select 2 union all
select 3 union all
select 5

insert into @temp_c
select 1 union all
select 2 union all
select 4

insert into @temp_d
select id from @temp_a
union
select id from @temp_b
union
select id from @temp_c

select *
from @temp_a as a
    inner join @temp_b as b on b.id = a.id
    inner join @temp_c as c on c.id = a.id
    right outer join @temp_d as d on d.id = a.id

id          id          id          id
----------- ----------- ----------- -----------
NULL        NULL        NULL        1
2           2           2           2
NULL        NULL        NULL        3
NULL        NULL        NULL        4
NULL        NULL        NULL        5

So if you switch to the left join, results will not be the same.

select *
from @temp_d as d
    left outer join @temp_a as a on a.id = d.id
    left outer join @temp_b as b on b.id = d.id
    left outer join @temp_c as c on c.id = d.id

id          id          id          id
----------- ----------- ----------- -----------
1           1           NULL        1
2           2           2           2
3           3           3           NULL
4           4           NULL        4
5           NULL        5           NULL

The only way to do this without the right join is to use common table expression or subquery

select *
from @temp_d as d
    left outer join (
        select *
        from @temp_a as a
            inner join @temp_b as b on b.id = a.id
            inner join @temp_c as c on c.id = a.id
    ) as q on ...