Re: record identical operator

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От Stephen Frost
Тема Re: record identical operator
Дата
Msg-id 20131004010959.GV2706@tamriel.snowman.net
обсуждение исходный текст
Ответ на Re: record identical operator  (Hannu Krosing <hannu@krosing.net>)
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* Hannu Krosing (hannu@krosing.net) wrote:
> The main exposed implementation detail of this operator is that it is
> very fast and can be recommended to be used at user level for speeding
> up equal query like this
>
> SELECT * FROM t WHERE <guaranteed equal> or <equal>
>
> where the plain <equal> will only be called when fast <guaranteed equal>
> fails.

Yeah, this would be exactly the kind of misuse that we will need to be
prepared to support with these new operators.  If this is actually
faster/better/whatever, then we should be implementing it in our
conditional handling, not encouraging users to create hacks like this.

> a bit similar to how you can cut down on index size on long text fields by
> indexing their hashes and then querying
>
> SELECT * FROM t
>  WHERE hashtext(verylongtext) = hashtext(sample)
>     AND verylongtext = sample

This case clearly requires a great deal more thought and consideration
on the DBA's side and is also a lot more obvious what it's doing than
having 'where x *= 123 or x = 123'.
Thanks,
    Stephen

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