1. Exploring common table expressions
We need to go deeper
Exploring common table expressions
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Evaluations
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5. We need to go deeper: Exploring CTEs
Daniel Hutmacher
SQL Server developer and independent contractor by day.
Spinning instructor by night.
I love coffee, travel, cycling, loud music and making SQL Server queries go really fast. Like, stupid-fast.
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6. We need to go deeper: Exploring CTEs
Common table expressions
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7. We need to go deeper: Exploring CTEs
Script 01
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8. We need to go deeper: Exploring CTEs
CTEs are not materialized
A common table expression is a glorified view
It won’t materialize
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9. We need to go deeper: Exploring CTEs
CTEs in sequence
You can put multiple CTEs in a statement, separated by commas.
You can even UPDATE or DELETE in a CTE.
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10. We need to go deeper: Exploring CTEs
Recursive CTEs
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11. We need to go deeper: Exploring CTEs
Script 03
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12. We need to go deeper: Exploring CTEs
Recursive CTEs
Anchor
Recursion
Stop condition (optional)
OPTION (MAXRECURSION) (optional)
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13. We need to go deeper: Exploring CTEs
Script 04
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14. A simple CTE
Anchor
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15. A simple CTE
Recursion
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16. A simple CTE
Stop condition
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17. The Fibonacci series example
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18. The Fibonacci series example
recursion=0
a=0, b=1
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19. The Fibonacci series example
recursion=0
a=0, b=1
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20. The Fibonacci series example
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21. The Fibonacci series example
recursion=recursion+1
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22. The Fibonacci series example
Do this...
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23. The Fibonacci series example
Do this...
WHERE a<
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24. The Fibonacci series example
Do this...
a=b, b=a+b
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25. The Fibonacci series example
recursions<100 ?
If not, crash and burn.
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26. The Fibonacci series example
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27. The Fibonacci series example
rinse, repeat...
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28. We need to go deeper: Exploring CTEs
What can we do with recursive CTEs?
Number series
String parsing (like split/merge)
Hierarchies
Dependency trees
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29. We need to go deeper: Exploring CTEs
Script 05-09
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30. We need to go deeper: Exploring CTEs
Bonus: can recursive CTEs be made parallel?
Script 10
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31. We need to go deeper: Exploring CTEs
Questions!
Twitter: @dhmacher
Blog: sqlsunday.com
Old-school:
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