Why Creating an Index Can Slow Down A Query (1 hour 30 minutes)

You can’t always create the perfect index for every query

But sometimes, performance can go badly wrong if SQL Server has an imperfect index for an query.

In this session, I show you a query whose performance regresses after you add a nonclustered index. Your challenge is to figure out why the query got slower.

Try your hand at speeding up the query by tuning the TSQL. Afterward, I explore the query execution plan with you and walk you through multiple potential solutions, showing the pros and cons of each one.

Course scripts and sample execution plans are here: https://github.com/LitKnd/SQLWorkbooks/tree/main/why_creating_an_index_can_slow_down_a_query

This course features closed captions in English for each video, plus a written transcript in each lesson.