1. Indexing Fundamentals
Kathi Kellenberger
Kellenberger Consulting, LLC

2. Who am I? Teacher Author @auntkathi http://auntkathisql.com
Beginning T-SQL
Expert T-SQL Window Functions
Beginning SSRS
Consultant
@auntkathi

3. The problem…. Our application is slow, and we don’t know why.
We are seeing lots of timeouts.
There is something wrong with our SQL Server; it used to be fast.
We have indexes, but we don’t know if they are the right ones.

4. What they have tried Added processors Upgraded storage
Added random indexes

5. Make SQL Server work less
Table

6. Make SQL Server work less
Index

7. Find My Number Game

8. Two types of tables
Heaps
Clustered Indexes

9. Heaps M S D X A T A

10. Clustered Index M D T A S X A D M S T X

11. Clustered Index M Non-Leaf Levels D T Contain the key A S X Leaf Level
Contains the key
other columns, and possibly a Uniquifier

12. Clustered Indexes Best Practices
Narrow
Unique
Never changing
Incrementing*
Based on workload
*Subject to debate

13. Two types of indexes
Clustered Index
Nonclustered Index

14. Nonclustered Index M Non-Leaf Levels D T Contain the key A S X
Contains the key,
Pointer to the table
row, and included
columns

15. Pointer to table row Clustered index – Cluster Key
Heap – RID (row identifier)

16. Column order
LastName
FirstName
City

17. Covering index

18. SARGability

19. SARGability Causes Function applied to column
LIKE with leading wildcard (%)
NOT LIKE
No filter on leading column
Implicit conversions

20. Nonclustered Index Best Practices
Can add up to 999, but try to stay at 10 or less indexes per table
Foreign keys
Common WHERE clause columns
Use workload to tune
Filter before joining columns
Take advantage of included columns