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copied!<p>Yes, you can only have a single clustered index per table - the data is physically arranged by that index, so you cannot have more than one.</p> <p>I would however not advise to use a composite clustered index. Why? Because the clustered index should always be:</p> <ul> <li>as small as possible - INT with 4 byte is perfect</li> <li>stable - never change, so you don't have rippling updates through all your indices</li> <li>unique - otherwise, SQL Server will have to "uniquify" your entries with artifical 4-byte values</li> <li>optimal would be: ever increasing</li> </ul> <p>INT IDENTITY is perfect as a clustered index - I would advise you keep it that way.</p> <p>The clustered index column (or set of columns) is also added to each and every entry of each and every nonclustered index on that same table - so if you make your clustered index large, 20, 50 bytes or more, you begin to be wasting a lot of space - on disk and in your server's memory, which generally degrades your system performance.</p> <p>Read all about clustered indices and what they should be to be good clustered indices here:</p> <ul> <li><a href="http://www.sqlskills.com/BLOGS/KIMBERLY/post/GUIDs-as-PRIMARY-KEYs-andor-the-clustering-key.aspx" rel="noreferrer">GUIDs as PRIMARY KEYs and/or the clustering key</a></li> <li><a href="http://sqlskills.com/BLOGS/KIMBERLY/post/The-Clustered-Index-Debate-Continues.aspx" rel="noreferrer">The Clustered Index Debate Continues...</a></li> <li><a href="http://www.sqlskills.com/BLOGS/KIMBERLY/post/Ever-increasing-clustering-key-the-Clustered-Index-Debateagain!.aspx" rel="noreferrer">Ever-increasing clustering key - the Clustered Index Debate..........again!</a></li> </ul>

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