Hierarchies are the bread and butter of most business applications and you find them almost everywhere: * Product Categories * Sales Territories * Calendar and Time Even when there is a big need from a business perspective, the solutions in relational databases are still sort of awkward. Since Version 2008 SQL Server makes live a bit easier with data type hierarchyid. To make use of aggregations you have to master GROUP BY clauses GROUPING SETS, CUBE, ROLLUP, WITH CUBE, or WITH ROLLUP as well. If you want to query of self-referenced tables you need a clear understanding of loops and common table expressions (CTE). Join this session for a journey through best practices to model your hierarchies and handy scripts to transform your hierarchies into useful information. We will have fun playing around with a sample database based on G. R. R. Martin’s famous “Game of Thrones”.

1. A Game of Hierarchies
From GROUP BY to Recursive CTEs

2. Thanks you our PLATINUM sponsors

3. Thanks you our GOLD and SILVER sponsors

4. Welcome to SQL Saturday Denmark

6. Introduction
Markus Ehrenmüller-Jensen
Business Intelligence Architect
SQL Server 2005 - 2016
BI Developer
Database Developer
Database Admin
@MEhrenmueller
/markus-ehrenmueller
markus.ehrenmueller@gmail.com
sqlederhose.wordpress.com

7. Every fool loves to hear that he’s important.
Tyrion Lannister (A Dance with Dragons)

8. Valar Morghulis
All men must die

9. Valar Dohaeris
All men must serve

10. Agenda
Aggregation, GROUP BY & OVER()
Several columns in one table
Several tables
Self-join in table
HierarchyID

11. Aggregations
Aggregate Functions
COUNT, SUM, MIN, MAX, AVG
GROUPING, GROUPING_ID
STDEV, STDEVP, VAR, VARP
COUNT_BIG, CHECKSUM_AGG
GROUP BY
ROLLUP
CUBE
GROUPING SET
OVER()
PARTITION BY
ORDER BY

12. Demo-Query

13. Aggregations

14. Aggregations
SELECT
POIName,
RegionName,
ContinentName,
WorldName,
COUNT(*) as
CountOfSomething
FROM
dbo.GoT_POI
GROUP BY
POIName,
RegionName,
ContinentName,
WorldName
ORDER BY
WorldName,
ContinentName,
RegionName,
POIName;

15. OVER()

16. OVER(PARTITION
BY WorldName)
OVER(PARTITION
BY RegionName)
OVER(PARTITION
BY POIName)
OVER(PARTITION
BY ContinentName)

17. GROUP BY ROLLUP 1/2
GROUP BY ROLLUP (
RegionName,
ContinentName,
WorldName
)
Region, Continent, World
Region, Continent
Region
()

18. GROUP BY ROLLUP 2/2
GROUP BY ROLLUP (
WorldName,
ContinentName,
RegionName
)
World, Continent, Region
World, Continent
World
()

19. GROUP BY CUBE 1/2
GROUP BY CUBE (
RegionName,
ContinentName,
WorldName
)
Region, Continent, World
Region, Continent
Region, World
Continent, World
Region
Continent
World
()

20. GROUP BY CUBE 2/2
GROUP BY CUBE (
WorldName,
ContinentName,
RegionName
)
Region, Continent, World
Region, Continent
Region, World
Continent, World
Region
Continent
World
()

21. GROUP BY GROUPING SETS
GROUP BY GROUPING SETS (
(RegionName, ContinentName,
WorldName),
(RegionName, ContinentName),
(RegionName, WorldName),
(ContinentName, WorldName),
(RegionName),
(ContinentName),
(WorldName),
()
)
Region, Continent, World
Region, Continent
Region, World
Continent, World
Region
Continent
World
()

22. How to implement Hierarchies in SQL Server?
Several columns in one table
Several tables
Self-join in table
HierarchyID

23. Several columns in one table
Eg. CityName, RegionName, ContinentName
Denormalized
Advantage
No joins needed
Disadvantage
Redundancy
Rather limited in the amount of groups/levels

24. Several columns in one table

25. Several tables
Eg. City.Name, Region.Name, Continent.Name
Normalized
References a row in another table
Advantage
No redundancy
Disadvantage
Joins needed
Rather limited in the amount of groups/levels

26. Several tables

27. Querying several tables

28. Self-join in table
Eg. Family.ID, Family.FatherID
References different row in the very same table
Advantage
Unlimited in the amount of levels
No redundancy
Disadvantage
Joins needed
Complex queries (Loops, recursive CTE)

29. Self-join in table

30. Querying a self-join table: Basic

31. Family Affairs
Child & Father
All descendants & all ascendants
X generations only
Grandfather & grandson
Ancestor & youngest generation
Uncles & aunts
Full family tree

32. I never bet against my family.
Tyrion Lannister (A Game of Thrones)

33. Demo-Query

34. Querying a self-join table through
recursive CTE

35. HierarchyID
Available since SQL Server 2008
Codes position within a hierarchy
Offers methods to access hierarchy attributes
Does not guarantee uniqueness
No foreign key constraints between nodes

36. Wrap up
Aggregation, GROUP BY & OVER()
Several columns in one table
Several tables
Self-join in table
HierarchyID

37. What John Snow knows
nothing (Source: Ygritte)

38. Resources
BOL: Using GROUP BY with ROLLUP, CUBE, and GROUPING
SETS
https://technet.microsoft.com/en-us/library/bb522495(v=sql.105).aspx
Itzik Ben-Gan (2015), T-SQL Querying, Microsoft Press
https://www.microsoftpressstore.com/store/t-sql-querying-
9780735685048
Steve Stedman (2015), Advanced CTE
http://stevestedman.com/2015/06/24-hours-of-pass-advanced-cte-
presenation/

39. Questions?
Markus Ehrenmüller-Jensen
Business Intelligence Architect
SQL Server 2005 - 2016
BI Developer
Database Developer
Database Admin
@MEhrenmueller
/markus-ehrenmueller
markus.ehrenmueller@gmail.com
sqlederhose.wordpress.com

40. Please review the event and sessions
 EVENT  SESSION
2016-09-
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