3 where are my keys - sql explore
- 1. Where Are My Keys?Ami Levin | CTO | DBSophic LTD
- 2. Session GoalsA revisit to some of the fundamental design principals of relational databases: Normalization rules, key selection, and the controversies associated with these issues from a very practical, hands-on perspective, with special emphasis on some surprising performance issues that may arise from sub-optimal selection of keys...
- 4. Normalization“A relation whose domains are all simple can be represented in storage by a two-dimensional column homogeneous array of the kind discussed above. Some more complicated data structure is necessary for a relation with one or more non-simple domains. For this reason (and others to be cited below) the possibility of eliminating non-simple domains appears worth investigating. There is, in fact, a very simple elimination procedure, which we shall call…normalization”
- 5. 1st Normal FormThere's no top-to-bottom or left-to-right ordering to the rows and columnsThere are no duplicate rowsEvery row-column intersection contains exactly one valueAll columns are regular
- 7. 2nd Normal FormR is in 1st Normal Form (1NF).Given any candidate key K and any attribute A that is not a constituent of a candidate key, A depends upon the whole of K rather than just a part of it.
- 9. 3rd Normal FormR is in second normal form (2NF)Every non-prime attribute of R is non-transitively dependent on every candidate key of R.A transitive dependency is a functional dependency, in which X -> Z (X determines Z) indirectly, by virtue of X -> Y and Y -> Z.
- 10. 3rd Normal Form
- 11. KeysSimpleComposite Candidate Primary Artificial / Surrogate IntelligentNatural
- 12. The DebateTo ID or not to ID?IDENTITY (1,1) PK vs. Natural key
- 13. Pro ArtificialIn some cases, no natural key exists and an artificial key is the only option.Examples?
- 14. Pro ArtificialNatural keys can change. Artificial keys never change.How Often?Cascading referential constraintsArtificial keys can change
- 15. Pro ArtificialNatural keys may become very long and complex.Get longer with each level900 Bytes limit in SQL ServerMulti-column Joins
- 16. Pro ArtificialArtificial keys improve performance. Simpler join predicatesEver increasing clustering effectShort keys = Smaller DB = Faster (?)
- 17. Pro ArtificialArtificial keys reduce clustered index fragmentation. All types of artificial keys?Minimize maintenance down timeWhat about deletes?What about non-clustered indexes?
- 18. Pro NaturalNatural keys have business meaning.Artificial keys are logically never queried for
- 19. Pro NaturalQueries on tables using natural keys require fewer joins.The more familiar and meaningful the key, the less joins are required“Bypass” joins across levels
- 20. Pro NaturalData consistency is maintained explicitly when using natural keys.Artificial keys enable logical duplicates
- 21. Pro NaturalNatural keys eliminate potential physical clustering performance issues.Contention for clustered regions
- 22. Less Mentioned IssuesArtificial keys are the de-facto standard.ORM generate artificial keysLINQ doesn’t cache composite key rows
- 23. Less Mentioned IssuesData statistics and optimizations.Statistics on artificial keys are useless for parameter sniffingSelectivity estimations on composite key statistics are less accurate
- 24. Less Mentioned IssuesModularity and portability.Migration to other platformsMerging with other databases
- 25. Less Mentioned IssuesSimplicity and aesthetics.
- 26. Demo Design SpecURLCountry and city of ownerCountry ISO code needed by applicationData consistency is crucial
- 28. Ask Yourself…Is there a natural key that I can use as PK? Are there a few natural candidates? Which one is the simplest and most familiar?How stable is it?How will it be used logically?What will be the table physical usage patterns?What are the common query types for this table?
- 29. For More InformationA Relational Model of Data for Large Shared Data Banksby E. F. CODD.The Relational Model for Database Management: Version 2 by E.F. Codd. An introduction to database systemsby C.J Date. Database in Depth: Relational Theory for Practitionersby C.J Date.The Database Relational Model: A Retrospective Review and Analysisby C.J Date.Joe Celko's Data and Databases: Concepts in Practice by Joe Celko.Joe Celko's SQL for Smarties, Fourth Edition: Advanced SQL Programmingby Joe Celko.Database Modeling and Design, Fifth Edition: Logical Designby Toby J. Teorey, Sam S. Lightstone, Tom Nadeau, and H.V. Jagadish.Pro SQL Server 2008 Relational Database Design and Implementationby Louis Davidson, Kevin Kline, Scott Klein, and Kurt Windisch.
- 30. Where Are My Keys?Q&A