问题
Ok here is a non clustered index features
Now as you can see Id is the Identity column which is primary key and clustered. I can either include it into the index columns and mark index as unique or not include it to the index itself and add it as included columns.
Which one should be selected and why ? thank you
回答1:
The clustered key is automatically included in the nonclustered index, whether you include it explicitly or not. In other words - don't include it, unless you need to use a predicate that filters on the clustered key and then a couple of other columns (in that order) - in that case it may make sense to force it as the first column, as it'll otherwise be stored physically as the last column.
来源：https://stackoverflow.com/questions/14349260/should-primary-key-clustered-index-columns-added-to-the-non-clustered-indexes