Introduction to Indexes

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Introduction to Indexes

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e-ghetto SSChasing Mays Points: 616 More actions · Answer 1

GilaMonster (7/4/2012)
For seeking, for range scans, for supporting an order by.

Oh, I didn't have the ORDER BY clause in mind yet. Thanks, it's more clearly now.

So, if I my query returns the records in the descending order - it is better to create the index column also in the same order ("DESC"), right?

paul.knibbs SSCoach Points: 15320 More actions · Answer 2

GilaMonster (7/4/2012)
For seeking, for range scans, for supporting an order by. Not ever for returning rows in the index order without an order by specified. That was quoted a bit out of context (context being ordering of returned rows without an order by)

Would it potentially make a difference to the amount of fragmentation caused by adding new items to the index? e.g. if your index key is a value that will generally *decrease*, would you get a less fragmented index by declaring it DESC?

Gail Shaw SSC Guru Points: 1004504 More actions · Answer 3

Maybe. Will it be a big difference and will the reduction in fragmentation affect query performance? Depends on other factors (frequency of inserts, type of queries, etc)

Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

sanjaydut26 SSCommitted Points: 1968 More actions · Answer 4

Thanks Gail, Awesome as always.

I have a small Confusion. Lets assume I have a table "Emp_details" with 4 columns-Emp_ID(primary key which creates clustered index by default), Name, Designation and Location and table has a million rows.
How does index works when i query table with where condition on "Name" column as shown below.

SELECT * FROM Emp_details where Name='ABC'

Thanks in Advance
Sanjay

JacekO SSCertifiable Points: 6610 More actions · Answer 5

The way you have it no index is used when this query is executed. You need an index on column Name

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