Optimize nested joins.

Hi,

If we have a query like the following :

select * from a left join b on a.id1= b.id2,

We can easily optimize by making a projection of a sorted by id1 and a projection of b sorted by id2(thus forcing a more efficient merge join).

But if we have a query like the following :

select * from (select * from a left join b on a.id1= b.id2) as c left join d on c.id1 = d.id4.

How would we proceed ? How do we ensure merge joins in this case ? We can make a projection of d sorted by id4, projection of a sorted on id1 and projection of b sorted by id2, but this does not ensure a merge join.

Thanks