Indexes and subqueries

I'm using 6.4.2 and I have the same problem as noted in previous mails in
the list archives but I can't find a coherent answer to the problem.

I need:

select * from sometable
where somefield in (select anotherfield from anothertable)

if I do:

select * from sometable where somefield in ('a','b','c');

explain uses the indexes i have created on sometable.somefield, when I use
the subquery a linear search is done.

Up till now I have handeled this by running the subquery in perl or tcl
and creating the quoted list and this works fine. However, now I have a
case where the query created in this way is longer than the 8192 bytes
allowed.

Now I need one of 2 solutions:

1) Is there any way I can let the subquery use the index?

or

2) How difficult/safe is it to change the max query length?

Your help will he HIGHLY appreciated!

Anton

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