1. Why should I care about SQL, if I have ORM?
Denis Reznik
Why should I care about SQL, if I have ORM?

2. Thank you to our AWESOME sponsors!

3. About Me Denis Reznik Kyiv, Ukraine Data Architect at Intapp, Inc.
Microsoft Data Platform MVP
Co-Founder of Ukrainian Data Community Kyiv (PASS Chapter)
PASS Regional Mentor, Central and Eastern Europe
Co-author of “SQL Server MVP Deep Dives vol. 2”

4. Agenda
.Net ORM History (how I remember it) Simple Queries Column List Lazy Load Data Types Data Modification Complex Query Parameter Sniffing The Main Thing to Keep in Mind

5. ORM History which I remember
ADO.NET
Data Sets (not too bad)
LLBL Gen, NHibernate (better than data sets)
LINQ to SQL (Awesome!)
Entity Framework. Should be even more awesome!
Entity Framework is more powerful than L2S
Entity Framework Code First
Entity Framework is not so good? So what?

6. Simple Query
SELECT * FROM Users WHERE Id = 1

7. Simple Query
Demo

8. Column List

9. Column List
Demo

10. Lazy Load

11. … … Index Seek SELECT * FROM Users WHERE Id = 523 1 .. 1M 2K+1 .. 4K
1M-2K .. 1M …
,5K
1,5K K …

12. … … Index Range Scan SELECT * FROM Users WHERE Id BETWEEN 700 AND 1700
1 .. 2K
2K K
1M-2K .. 1M …
,5K
1,5K K …

13. … … Index Scan SELECT * FROM Users 1 .. 1M 2K+1 .. 4K 1M-2K .. 1M
,5K
1,5K K …

14. Can Scan Outperform Seek?
SELECT user_id FROM Statuses
WHERE user_id < 2000 …
Leaf-Level Rows:
Leaf-Level Pages: 2970
Rows on Page (Avg): 356
Index Depth: 3
One Page Seek: 356*3= 1068
1068*3=3204 > 2870 => Row by Row Seek of 3 pages is heavier than full index scan
(For this concrete case)

15. Lazy Load
Demo

16. Data Types

17. Data Types
Demo

18. Data Modification

19. Data Modification
Demo

20. Complex Query

21. What does it mean “Complex Query” ?

22. What does it mean “Complex Query” ?

23. Complex Query
Demo

24. Parameter Sniffing

25. Parameter Sniffing - Stored Procedure
Query Processor
EXEC = 1
EXEC = 22
SQL Server Cache
Procedure cache
Procedure cache
Query executes using the query plan created for
@UserId = 1
Plan created and cached for the
@UserId = 1

26. Parameter Sniffing - Parametrized Query
Query Processor
sp_executesql N'SELECT * FROM Users WHERE Id int', 1
SELECT * FROM Users WHERE Id
SELECT * FROM Users WHERE Id
sp_executesql N'SELECT * FROM Users WHERE Id int', 22
SQL Server Cache
Procedure cache
Procedure cache
Plan created and cached for the
@Id = 1
Query executes using the query plan created for
@Id = 1

27. Dynamic SQL – Multiple Plans
Query Processor
SELECT * FROM Users WHERE Id = 1
SELECT * FROM Users WHERE Id = 22
SQL Server Cache
SELECT * FROM Users WHERE Id = 1
Procedure cache
Procedure cache
Procedure cache
Query executed using the query plan, created for the first query.
New query plan created and cached. Query executed using newly created plan.
New query plan again created and cached. Query executed using newly created plan.

28. Parameter Sniffing
Demo

29. The Main Thing to Keep in Mind

30. Life without ORM (Entity Framework)
Some Magic
Query
Result Set
32 |

31. Life with ORM (Entity Framework)
Some Magic
Application Code
SQL Query
Some Magic
Result Set
33 |

32. Life with micro-ORM (Dapper)
Some Magic
Query
Result Set
34 |

33. Summary ORM is really nice tool
But it still requires strong SQL Server background
Databases and ORMs are changing very fast
Few Advices
Sometimes check the generated SQL and its query plan
For complex queries consider raw SQL anyway
Consider using Dapper
Invest your time to learn database internals
ORM should not save you from learning SQL and SQL Server

34. Thank You! Denis Reznik Twitter: @denisreznik
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