February 27, 2014 at 4:33 pm
Greetings,
One simple question regarding the concept behing the Covering Indexes technique. I understood the explanation and purpose (to improve performance of the query plan by not needing to perform additional lookups through the heap or clustered table), but one thing bothers me: How is the data retrieved stored at the nonclustered index, since the leaf level contains only clustering keys or row locators? I thought this was possible only with the clustered index that has actually data pages on the leaf level.
Thanks
February 27, 2014 at 4:49 pm
Included columns are stored alongside the clustered index key lookup information at the leaf level, thus widening the storage for that index. It's a powerful tool, but easy to abuse.
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