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sql-serverprimary-keyuniqueidentifier
Chris S
Chris S

Reputation: 65426

Clustered primary key on unique identifier ID column in SQL Server

If your ID column on a table is a unique identifier (Guid), is there any point creating a clustered primary key on the ID column?

Given that they are globally unique, how would the sorting work?

Upvotes: 3

Views: 5937

Answers (4)

Learning
Learning

Reputation: 8175

The idea of having a sorted index is very good in itself as searching then becomes very efficient.

The problem however is that in case of a GUID one never searches with "WHERE GUID = xyz". So the whole concept is wasted. So I would suggest to rather have a clustered index on a column which is used most often as a SARG to increase the query efficiency.

Upvotes: 1

Frederik Gheysels
Frederik Gheysels

Reputation: 56934

Putting a clustered index on a guid column is not such a good idea (unless you're making use of sequential guids).

The clustered index determines the physical order of how the records are stored.
This means that, if you put a clustered index on a column that does not sequentially grow, SQL Server will have some work making sure that the records are correctly ordered physically when you insert new records.

Upvotes: 3

Anton Gogolev
Anton Gogolev

Reputation: 115711

GUIDs as they are are terrible for performance since they are effectively random values (this "breaks" clustered index), and they are awful for indexes, since less entries fit on a single page/extent (SQL Server terms). SQL Server 2005 introduces newsequentialid() which helps solving first problem.

Upvotes: 5

Igor Brejc
Igor Brejc

Reputation: 19004

I strongly advise against using clustered Guid key... We had big performance issues on SQL server because of such poor design a few years ago.

Also check out: Improving performance of cluster index GUID primary key

Upvotes: 5

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