Indexing every column in a table

Question

I have a couple of questions regarding MySQL indexing:

1) Is there any speed increase when indexing a table stored in memory?

2) When searching my table I ma

Answer 1

1) Yes, of course.
2) No, it doesn't defeat the purpose of index. Just remember that mysql can't use more than 1 index per table and that adding more indexes slowdowns insert/update/delete operations. So avoid creating indexes that aren't used, create multicolumn indexes that matches your queries best instead.