Обсуждение: Unique Index vs. Unique Constraint

Does a Unique Constraint build a unique index?

What is the difference?

Thanks,
Thomas LeBlanc

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On Fri, 10 Oct 2003 13:59:38 -0500, "Thomas LeBlanc"
<thomasatiem@hotmail.com> wrote:
>Does a Unique Constraint build a unique index?

Yes.

>What is the difference?

A constraint is an abstract concept, an index is an implementation
detail.

Servus
 Manfred

On Fri, 10 Oct 2003, Thomas LeBlanc wrote:

> Does a Unique Constraint build a unique index?
>
> What is the difference?

None that I know of.

Then what is the difference in these two statements?

alter table Table1
  add constraint Table1_UC1
  unique (Field1, Field2)

and

create unique index Table1_Field1Field2
   on Table1 (Field1, Field2)


Thanks,
Thomas LeBlanc




>From: Dennis Gearon <gearond@fireserve.net>
>To: Thomas LeBlanc <thomasatiem@hotmail.com>
>Subject: Re: [GENERAL] Unique Index vs. Unique Constraint
>Date: Fri, 10 Oct 2003 15:16:12 -0700
>
>Uniquely so!
>
>Thomas LeBlanc wrote:
>
>>Does a Unique Constraint build a unique index?
>>
>>What is the difference?
>>
>>Thanks,
>>Thomas LeBlanc
>>
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>>Get a FREE computer virus scan online from McAfee.
>>http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963
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>

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scott.marlowe wrote:

> On Fri, 10 Oct 2003, Thomas LeBlanc wrote:
>
>> Does a Unique Constraint build a unique index?
>>
>> What is the difference?
>
> None that I know of.

A different implementation of UNIQUE constraint might allow
deferrability, what our index solution does not ... yet.


Jan

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