How many colums should a index contain?

[John . H]

I have two tables and I must do :
select `id`,`bid`,`title`,`link`,`bname` from table1 where `bid` in
( ...this is a subquery in table2  )
should I create a index (`id`,`bid`,`title`,`link`,`bname`) so that my query
will take less time
or should a index contain so many colums?