Window functions are powerful analytic functions built into SQL Server. SQL Server 2005 introduced the core window ranking functions, and SQL Server 2012 added time and statistical percentage window functions. These functions allow for advanced variable creation, and are of direct benefit to people creating features for data science. This talk will also recommend further reading on this topic. The slide deck contains a link to the code on GitHub.

1. Window Functions for
Data Science
MARK TABLADILLO PH.D.
MICROSOFT MVP – ATLANTA, GA
FEBRUARY 2016

2. Abstract
Window functions are powerful analytic functions built into
SQL Server. SQL Server 2005 introduced the core window
ranking functions, and SQL Server 2012 added time and
statistical percentage window functions. These functions
allow for advanced variable creation, and are of direct
benefit to people creating features for data science. This
talk will also recommend further reading on this topic.
Required for Certification

3. What is a “Window”?
Answer: A set of rows defined by the OVER clause
Set One
Set Two
Set Three
ORDER BY
Set One
Set Two
Set Three
PARTITION BY

4. What is a “function”?
Function Example
Ranking ROW_NUMBER, RANK, DENSE_RANK, NTILE
Aggregate MIN, MAX, AVG, SUM, COUNT, STDEV, STDEVP, VAR, VARP
CHECKSUM_AGG, COUNT_BIG
Analytic LAG, LEAD, FIRST_VALUE, LAST_VALUE, PERCENT_RANK, PERCENTILE_CONT,
PERCENTILE_DISC, CUME_DIST
GROUP BY not required

5. Demo: Ranking

6. What is a “Window”?
Answer: A set of rows defined by the OVER clause
Set One
Set Two
Set Three
ORDER BY
Set One
Set Two
Set Three
PARTITION BY

7. What is a “function”?
Function Example
Ranking ROW_NUMBER, RANK, DENSE_RANK, NTILE
Aggregate MIN, MAX, AVG, SUM, COUNT, STDEV, STDEVP, VAR, VARP
Analytic LAG, LEAD, FIRST_VALUE, LAST_VALUE, PERCENT_RANK, PERCENTILE_CONT,
PERCENTILE_DISC, CUME_DIST
GROUP BY not required

8. Order please

9. Demo: Aggregate

10. What is a “Window”?
Answer: A set of rows defined by the OVER clause
Set One
Set Two
Set Three
ORDER BY
Set One
Set Two
Set Three
PARTITION BY

11. What is a “function”?
Function Example
Ranking ROW_NUMBER, RANK, DENSE_RANK, NTILE
Aggregate MIN, MAX, AVG, SUM, COUNT, STDEV, STDEVP, VAR, VARP
Analytic LAG, LEAD, FIRST_VALUE, LAST_VALUE, PERCENT_RANK, PERCENTILE_CONT,
PERCENTILE_DISC, CUME_DIST
GROUP BY not required

12. Framing: Order Matters
Term Operators
ROWS = Physical Operator (faster) UNBOUNDED PRECEDING
UNBOUNDED FOLLOWING
N PRECEDING
N FOLLOWING
CURRENT ROW
RANGE = Logical Operator (slower) UNBOUNDED PRECEDING
UNBOUNDED FOLLOWING
CURRENT ROW (RANGE?)

13. Default Frame
First row of partition to current row

14. 1 2 3 4 5 6 7 8 9
Current Row
Unbounded FollowingUnbounded Preceding
4 Preceding
2 Following
1 Preceding 1 Following
ROW

15. Current Row
Unbounded Following
Unbounded Preceding
RANGE
1 2 3 4 5 6 7 8 9
12 23 34 45 50 50 50 50 65

16. Demo: Framing

17. What is a “Window”?
Answer: A set of rows defined by the OVER clause
Set One
Set Two
Set Three
ORDER BY
Set One
Set Two
Set Three
PARTITION BY

18. What is a “function”?
Function Example
Ranking ROW_NUMBER, RANK, DENSE_RANK, NTILE
Aggregate MIN, MAX, AVG, SUM, COUNT, STDEV, STDEVP, VAR, VARP
Analytic LAG, LEAD, FIRST_VALUE, LAST_VALUE, PERCENT_RANK, PERCENTILE_CONT,
PERCENTILE_DISC, CUME_DIST
GROUP BY not required

19. Demo: Analytic

20. Caveats Exist
But if Window Functions alone cannot do the job,
Then something else can

21. Logical Alternatives
 Common Table Expressions (CTEs)
 CROSS APPLY

22. Nondeterministic
Functions =
Not one unique
way to do the job
https://msdn.microsoft.com/en-
us/library/ms178091.aspx

25. Code
Available at https://github.com/marktab/windowfunctions2016