> From with amount of record in a table it's start to be usefull to have
> an index ?
> 100? 1000? 10000 ?
>
> Actually i thing about 200 ? maybe 1000 ?

I do remember an general estimation that tables with some few hundred
rows do not need index creation.

To be more specific you also have to consider the size of each row.

Without an index the select does scan all pages in table.

With an primary-key-index the select does scan presumably two pages from
index and an third page to read data. I do assume that the table is not
that small to fit all index information into an single page.

Without index UPDATE/INSERT/DELETE ist faster.

Without further knowledge I would estimate your table size at the edge
of indexing becoming important - you might have to run some benchmark to
decide.

Elmar