"Gail Shaw" <initialsurname@sentech sa dot com> wrote in message
news:48919ec6@news.povray.org...
>
> "Invisible" <voi### [at] devnull> wrote in message
> news:48917361$1@news.povray.org...
>
> > Although - and not many people seem to understand this part - indexes
> > make looking up *one* element much faster (if you index the right
> > thing). However, if you're doing to end up needing to process a large
> > percentage of the table anyway, it's actually faster to *not use* any
> > indexes there might be.
>
> Really? I'll go and discard everything I know about using indexes right
> away....

Sorry, that cam out a little snarkier than I intended.

Taking SQL Server as an example (so I can give specific numbers), if an
index does not contain all the columns required, the break point for use the
index or scan the table is around 1% of the table. If the index does contain
all the columns, then the index will be used whether 1 row is required or
the entire table.

It's not hard to demonstrate.

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