Difference in UNique Non-Clustered and Non-Clustered

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Difference in UNique Non-Clustered and Non-Clustered

VastSQL

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March 19, 2014 at 2:37 am

#396439

Hi Experts,
Is there any difference in unique Non-Clustered and Non-Clustered and non-clustered index. What is the effect of adding a non-clustered index to a unique column and creating a unique non-clustered index on the same column.

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Gail Shaw SSC Guru Points: 1004504 More actions · Answer 1

A nonclustered index that is defined as unique (CREATE UNIQUE NONCLUSTERED INDEX ...) enforces uniqueness on its key columns. A nonclustered index defined without the unique keyword doesn't.

Not that much more to it than that.

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
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VastSQL SSC-Dedicated Points: 36097 More actions · Answer 2

Thanks Gail..

I think the space used by non-unique non-clustered index is on higher side when compare to unique non-clustered index 111 vs 107.

Grant Fritchey SSC Guru Points: 398890 More actions · Answer 3

The optimizer will know that an index is unique and may use that as part of it's decision process when putting together the execution plan.

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