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1642

answers:

4

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?

+4  A: 

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: http://stackoverflow.com/questions/583001/improving-performance-of-cluster-index-guid-primary-key

Igor Brejc
+5  A: 

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.

Anton Gogolev
+3  A: 

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.

Frederik Gheysels
+2  A: 

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.

Learning
I think "WHERE GUID = xyz" is used a lot, in selecting single records. But ab "ORDER BY guid" would be very rare.
Henk Holterman