Ben Escoto writes:
> Thank you for the response. In which cases does DESC disable indexed
> sorting? Perhaps there is a a way around this for the time being?
> For instance, I noticed that although:
>
> SELECT * FROM sqmail.sequence_data WHERE sid = 16 ORDER BY sid DESC,id
> DESC LIMIT 10
>
> uses filesort,
>
> SELECT * FROM sqmail.sequence_data WHERE id < 100000 ORDER BY
> sid DESC,id DESC LIMIT 10
>
> does not and is quite fast. Somehow the optimizer is getting confused
> by the "sid = 16". I was thinking that perhaps there is some magic
> way of rephrasing the problem that MySQL would understand better.
> Failing that, what is the recommended way of making this query
> quicker? Should I insert another index, for instance called
> negative_id that is always (4294967296 - id) or something like that,
> so I can ORDER BY negative_id instead of ORDER BY id DESC?
>
> Thank you for any advice or suggestions you might have.
>
>
> --
> Ben Escoto
>
Hi!
Can you send me output of EXPLAIN for both queries.
Regards,
Sinisa
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