Indexing Fundamentals Kathi Kellenberger Kellenberger Consulting, LLC

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

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.

What they have tried Added processors Upgraded storage Added random indexes

Make SQL Server work less Table

Make SQL Server work less Index

Find My Number Game

Two types of tables Heaps Clustered Indexes

Heaps M S D X A T A

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

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

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

Two types of indexes Clustered Index Nonclustered Index

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

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

Column order LastName FirstName City

Covering index

SARGability

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

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