1. Simple tips for better data warehouse design
Michael Johnson

2. About me Michael Johnson Johannesburg SQL User Group Lead
@MikeJohnsonZA

3. What we will cover: Use surrogate keys One Fact table per process
Aesthetics
Indexing
Q & A

4. Primer
What is Dimensional modelling

5. Primer What is Dimensional modelling Date Dimension Fact Sales Person
Region
Dimension
Product
Dimension

6. Lets begin

7. #1 - Use Surrogate Keys Employee Number Employee Name Department …
John Smith
Finance
EMP0005
Peter Jackson
Sales
TMP0003
Mary Robins
Marketing
Time sheets number
Employee Number
Date
Hours …
2016JAN01
EMP0001
1 Jan 2016 8
2016JAN02
EMP0005
2016JAN03
TMP0003
10.5

8. #1 - Use Surrogate Keys
Reduce the size of fact tables

9. #1 - Use Surrogate Keys Employee Key Employee Number Employee Name
Department … 1
EMP0001
John Smith
Finance 2
EMP0005
Peter Jackson
Sales 3
TMP0003
Mary Robins
Marketing
Time sheets number
Employee Key
Date
Hours … 1 8 2 3
10.5

10. #1 - Use Surrogate Keys
Star join optimisation

11. #1 - Use Surrogate Keys Allow Slowly change Dimensions Employee Key
Effective date
Expiry date
Employee Number
Employee Name
Department … 1
EMP0001
John Smith
Finance 2
EMP0005
Peter Jackson
Sales 3
TMP0003
Mary Robins
Marketing

12. #1 - Use Surrogate Keys Allow Slowly change Dimensions Employee Key
Effective date
Expiry date
Employee Number
Employee Name
Department … 1
EMP0001
John Smith
Finance 2
EMP0005
Peter Jackson
Sales 3
TMP0003
Mary Robins
Marketing 4
Time sheets number
Employee Key
Date
Hours … 1 8
2642 4 11

13. One fact table per process

14. One fact table per process
Time Sheet Key
Employee Key
Date Key
Hours
123456
201 8

15. One fact table per process
Time Sheet Key
Employee Key
Date Key
Hours
Rate
Amount
123456
201 8
100
800
Time Sheet Key
Employee Key
Date Key
Invoice Key
Hours
Rate
Amount
123456
201 1 8
100
800

17. One fact table per process
Time Sheet Key
Employee Key
Date Key
Invoice Key
Hours
Rate
Amount
123456
201 1 8
100
800 2
-100
-800

18. One fact table per process
Time Sheet Key
Employee Key
Date Key
Invoice Key
Hours
Rate
Amount
123456
201 1 8
100
800 2
-100

19. One fact table per process
Time Sheet Key
Employee Key
Date Key
Invoice Key
Hours
Rate
Amount
123456
201 1 8
100
800 2
-100
-800

20. Aesthetics

21. Naming – Use descriptive names
[OrdQty] VS [Order Quantity]

22. Naming – don’t use legacy naming conventions
[Tbl_fact_sales] VS [Sales]

23. [DBO].[Fact_Orders] VS [Fact].[Orders]
Naming – Use schemas
[DBO].[Fact_Orders] VS [Fact].[Orders]

24. Use foreign keys but disable them

25. Quick Demo

26. Indexing fact tables

27. Indexing fact tables

29. Thank you
A big thank you to our sponsors, without them days like today would not happen.