Re: difference between a unique constraint and a unique index ???

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От Dave Cramer
Тема Re: difference between a unique constraint and a unique index ???
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Msg-id 694A5959-73AC-4C18-AA5F-489407A6CFDC@fastcrypt.com
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Ответ на Re: difference between a unique constraint and a unique index ???  (Tom Lane <tgl@sss.pgh.pa.us>)
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On 12-Nov-07, at 11:37 AM, Tom Lane wrote:

> Alvaro Herrera <alvherre@alvh.no-ip.org> writes:
>> Well, AFAIK the index with varchar_pattern_ops is used for LIKE
>> queries,
>> whereas the other one is going to be used for = queries.  So you
>> need to
>> keep both indexes.
>
> Given the current definition of text equality, it'd be possible to
> drop
> ~=~ and have the standard = operator holding the place of equality in
> both the regular and pattern_ops opclasses.  Then it'd be possible to
> support regular equality queries, as well as LIKE, with only the
> pattern_ops index.
>
That would be ideal. Having two indexes on the same column isn't
optimal.

Dave

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