Introduction to Indexes

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Introduction to Indexes

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e-ghetto SSChasing Mays Points: 606 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
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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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