1. T-SQL Window function deep dive part 2
Kathi Kellenberger
@auntkathi

2. What are window functions?
Nothing to do with Windows OS
Standard functionality added to T-SQL
Functions that operate on a set or window of rows
Always with an OVER clause (but sometimes you will see an OVER clause without a window function)
Always found in the SELECT and ORDER BY
Makes queries easier to write
Often better performance
What are window functions?

3. What are window functions?
2005
ROW_NUMBER(), RANK(), DENSE_RANK() and NTILE()
Window aggregates
2012
Framing
Enhanced window aggregates with ORDER BY
Analytic functions
Offset functions
What are window functions?

4. Execution Plan Operators

5. Execution Plan Operators

6. Execution Plan Operators

7. POC Index (from Itzik Ben-Gan)
Filtered column(s) + Partition column(s) + Order by column(s) + Covering columns(s)
Indexes

8. Window Aggregates Use caution with window aggregates
Pre-aggregate if possible
Older techniques might perform better
Window Aggregates

9. Default frame: RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
Better performance with ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
IMPORTANT: If ORDER BY column values are not unique, will get different results using RANGE
Framing

10. Performance

11. Performance

12. Summary POC index can help all window functions Use ROWS for framing
Use window aggregates (without ORDER BY) with caution
Summary

13. Resources Adam Machanic’s Big Adventure Script
king-big-adventure.aspx
My book: Expert T-SQL Window Functions
Itzik Ben-Gan’s book: Microsoft SQL Server 2012 High-Performance T-SQL Using Window Functions
Beginning T-SQL 3rd Edition by Kathi Kellenberger and Scott Shaw
Resources

14. Just like Jimi Hendrix …
We love to get feedback
Please complete the session feedback forms

15. SQLBits - It's all about the community...
Please visit Community Corner, we are trying this year to get more people to learn about the SQL Community, equally if you would be happy to visit the community corner we’d really appreciate it.