Re: index

On Jul 29, 1:18 pm, "Brian Selzer" <br...@xxxxxxxxxxxxxxxxxxx> wrote:
"David BL" <davi...@xxxxxxxxxxxx> wrote in message

news:f08bba46-7bd1-443e-97fd-fe07a9ec1a3f@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

On Jul 29, 10:45 am, "Brian Selzer" <br...@xxxxxxxxxxxxxxxxxxx> wrote:
"David BL" <davi...@xxxxxxxxxxxx> wrote in message
Physical duplication of data can be appropriate to increase read
performance at the expense of write performance. Indeed any secondary
index is a form of redundancy that hurts write performance.

Boosting read performance can be accomplished just as well with a
covering
non-clustered index as with a clustered index.

That is not always true. There could be an application involving a
query that uses the non-clustered index and also needs *all* the
additional data in the record. The additional seeks could mean the
read performance doesn’t meet the requirements.

If the index is a /covering/ index, then there is no need for the additional
read.

But then it won’t be a non-clustered index.
.

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