Suppose I am going to select in both ascending and desending order.

select * from foo order by a
select * from foo order by a desc

Is only one index for ascending order (default) sufficient, or I have to use 2
index, one ascend and the other desc?
create index foo_a on foo(a)
create desc index foo_a_d on foo(a)

Also is it possible to create a composite index on some ascending column and
some descending column, like equivalent of
create index foo_inx on foo(a , b desc, c)

--
regards,
bill