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 | | From: | Richard Huxton | | Subject: | Re: [SQL] OFFSET impact on Performance??? | | Date: | Thu, 20 Jan 2005 17:24:36 +0000 |
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 | Greg Stark wrote:
> "Andrei Bintintan" writes:
>
>
>>>If you're using this to provide "pages" of results, could you use a cursor?
>>
>>What do you mean by that? Cursor?
>>
>>Yes I'm using this to provide "pages", but If I jump to the last pages it goes
>>very slow.
>
>
> The best way to do pages for is not to use offset or cursors but to use an
> index. This only works if you can enumerate all the sort orders the
> application might be using and can have an index on each of them.
>
> To do this the query would look something like:
>
> SELECT * FROM tab WHERE col > ? ORDER BY col LIMIT 50
>
> Then you take note of the last value used on a given page and if the user
> selects "next" you pass that as the starting point for the next page.
Greg's is the most efficient, but you need to make sure you have a
suitable key available in the output of your select.
Also, since you are repeating the query you could get different results
as people insert/delete rows. This might or might not be what you want.
A similar solution is to partition by date/alphabet or similar, then
page those results. That can reduce your resultset to a manageable size.
--
Richard Huxton
Archonet Ltd
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