steam learn: relational database normal forms
TRANSCRIPT
August, 21st 2014
Relational Database Normal FormsDreams, inc case study
by Romain Francez
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Disclaimer
● Not only about showing good database design
● About understanding normal forms
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My Boss
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Started managing with that
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Started managing with that
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Aim
● Model that manages the business (employees, items,
…)
● Steps that might be needed to do as a business grow
whilst solving some problems
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Nomenclature
● Business Rules (BR)
○ Some normal forms take into account your business
logic
● Tables
○ Table name
○ Column name
○ Key
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SQL Normal Forms
● What is a Normal Form?
● What is the simplest data model?
● How to remove functional dependency?
● How to deal with join dependency?
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What is a Normal Form?
Set of rules for database design to minimise redundancy and to ensure consistency in insert/delete/update
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SQL Normal Forms
● What is a Normal Form?
● What is the simplest data model?
● How to remove functional dependency?
● How to deal with join dependency?
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1NF
EmployeeEmployee DreamCobb Rainy Downtown, Hotel, Snowy Mountain, LimboArthur Rainy Downtown, Hotel
Ariadne Rainy Downtown, Hotel, Snowy Mountain, Limbo
Eames Rainy Downtown, Hotel, Snowy MountainYusuf Rainy Downtown
BR1.1: Employees work on Dreams
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1NF
The domain of each attribute contains only atomic values, and the value of each attribute contains only a single value from that domain
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Atomic?
● Something that cannot be subdivided
● String, can be subdivided into substrings, but still
considered as atomic
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1NF
EmployeeEmployee DreamCobb Rainy Downtown, Hotel, Snowy Mountain, LimboArthur Rainy Downtown, Hotel
Ariadne Rainy Downtown, Hotel, Snowy Mountain, Limbo
Eames Rainy Downtown, Hotel, Snowy MountainYusuf Rainy Downtown
EmployeeEmployee DreamCobb Rainy DowntownCobb HotelCobb Snowy MountainCobb LimboArthur Rainy DowntownArthur HotelAriadne Rainy DowntownAriadne HotelAriadne Snowy MountainAriadne LimboEames Rainy DowntownEames HotelEames Snowy MountainYusuf Rainy Downtown
BR1.1: Employees work on Dreams
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SQL Normal Forms
● What is a Normal Form?
● What is the simplest data model?
● How to remove functional dependency?
● How to deal with join dependency?
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2NF
EmployeeEmployee Dream Risk LevelCobb Rainy Downtown MediumCobb Hotel MediumCobb Snowy Mountain HighCobb Limbo ExtremeArthur Rainy Downtown MediumArthur Hotel MediumAriadne Rainy Downtown MediumAriadne Hotel MediumAriadne Snowy Mountain HighAriadne Limbo ExtremeEames Rainy Downtown MediumEames Hotel MediumEames Snowy Mountain HighYusuf Rainy Downtown Medium
BR2.1: Dreams have a risk level
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2NF
Every non-prime attribute of the table is dependent on the whole of a candidate key
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Candidate Key?Colour
Colour Hex R G BRed FF0000 255 0 0
{Colour, Hex, R, G, B}{Colour}{Hex}{R, G, B}{Colour, Hex}{Colour, R, G, B}{Hex, R, G, B}
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Superkey
{Colour}or{Hex}
ColourColour Hex R G BRed FF0000 255 0 0
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2NF
EmployeeEmployee Dream Risk LevelCobb Rainy Downtown MediumCobb Hotel MediumCobb Snowy Mountain HighCobb Limbo ExtremeArthur Rainy Downtown MediumArthur Hotel MediumAriadne Rainy Downtown MediumAriadne Hotel MediumAriadne Snowy Mountain HighAriadne Limbo ExtremeEames Rainy Downtown MediumEames Hotel MediumEames Snowy Mountain HighYusuf Rainy Downtown Medium
DreamDream Risk LevelRainy Downtown MediumHotel Medium
Snowy Mountain HighLimbo Extreme
Employee_DreamEmployee DreamCobb Rainy DowntownCobb HotelCobb Snowy MountainCobb LimboArthur Rainy DowntownArthur HotelAriadne Rainy DowntownAriadne HotelAriadne Snowy MountainAriadne LimboEames Rainy DowntownEames HotelEames Snowy MountainYusuf Rainy Downtown
BR2.1: Dreams have a risk level
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Why Do Business Rules Matter?
Employee_DreamEmployee Dream Risk LevelCobb Rainy Downtown MediumCobb Hotel MediumCobb Snowy Mountain HighCobb Limbo ExtremeArthur Rainy Downtown MediumArthur Hotel MediumAriadne Rainy Downtown MediumAriadne Hotel MediumAriadne Snowy Mountain HighAriadne Limbo ExtremeEames Rainy Downtown MediumEames Hotel MediumEames Snowy Mountain HighYusuf Rainy Downtown Medium
2NF because the risk level now depends on the Employee and Dream
BR2.2: Each Employee is graded a risk level per Dream
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3NF
Dream
Dream Risk Level Minimum Preparation TimeRainy Downtown Medium 10Hotel Medium 10Snowy Mountain High 20Limbo Extreme 50
BR3.1: Each dream must have a minimum of preparation time depending on its risk level
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3NF
All the attributes in a table are dependent on the primary key and only on the primary key
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3NF
Dream
Dream Risk Level Minimum Preparation TimeRainy Downtown Medium 10Hotel Medium 10Snowy Mountain High 20Limbo Extreme 50
Risk
Risk Level Minimum Preparation TimeMedium 10High 20Extreme 50
DreamDream Risk LevelRainy Downtown MediumHotel Medium
Snowy Mountain HighLimbo Extreme
BR3.1: Each dream must have a minimum of preparation time depending on its risk level
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SQL Normal Forms
● What is a Normal Form?
● What is the simplest data model?
● How to remove functional dependency?
● How to deal with join dependency?
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4NF
Employee_DreamEmployee Dream SkillArthur Rainy Downtown DreamsArthur Rainy Downtown GunsArthur Hotel DreamsArthur Hotel GunsAriadne Rainy Downtown ArchitectureAriadne Hotel ArchitectureAriadne Snowy Mountain ArchitectureAriadne Limbo ArchitectureYusuf Rainy Downtown DreamsYusuf Rainy Downtown Sedatives
BR4.1: Employees have various skills
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4NF
Every non-trivial multivalued dependency in the table is a dependency on a superkey
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4NF
Employee_DreamEmployee Dream SkillArthur Rainy Downtown DreamsArthur Rainy Downtown GunsArthur Hotel DreamsArthur Hotel GunsAriadne Rainy Downtown ArchitectureAriadne Hotel ArchitectureAriadne Snowy Mountain ArchitectureAriadne Limbo ArchitectureYusuf Rainy Downtown DreamsYusuf Rainy Downtown Sedatives
Employee_SkillEmployee SkillArthur DreamsArthur GunsAriadne ArchitectureYusuf DreamsYusuf Sedatives
Employee_DreamEmployee DreamArthur Rainy DowntownArthur HotelAriadne Rainy DowntownAriadne HotelAriadne Snowy MountainAriadne LimboYusuf Rainy Downtown
BR4.1: Employees have various skills
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4NF
● {Employee} ->> {Dream}
● {Employee} ->> {Skill}
● Superkey: {Employee, Dream, Skill}
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5NF
BR6.1: Dreams have an IDBR6.2: 2 Dreams cannot have the same IDBR6.3: Dreams have a NameBR6.4: Dreams have a DescriptionBR6.5: Dreams have an Aim
BR2.1: Dreams have a risk level
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5NFDream_Name
Dream ID Name1 Rainy Downtown2 Hotel3 Snowy Mountain4 Limbo
Dream_RiskDream ID Risk Level
1 Medium2 Medium3 High4 Extreme
Dream_DescriptionDream ID Description
1 A regular city2 A classy Hotel3 A fortress4 Infinite raw subconscious
Dream_AimDream ID Aim
1 Go Deeper2 Go Deeper3 Plant Idea4 Escape
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5NF
Every non-trivial join dependency in the table is implied by the superkeys of the table
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5NF
DreamDream ID Name Risk Level Description Aim
1 Rainy Downtown Medium A regular city Go Deeper2 Hotel Medium A classy Hotel Go Deeper3 Snowy Mountain High A fortress Plant Idea4 Limbo Extreme Infinite raw subconscious Escape
Dream_NameDream ID Name
1 Rainy Downtown2 Hotel3 Snowy Mountain4 Limbo
Dream_RiskDream ID Risk Level
1 Medium2 Medium3 High4 Extreme
Dream_DescriptionDream ID Description
1 A regular city2 A classy Hotel3 A fortress4 Infinite raw subconscious
Dream_AimDream ID Aim
1 Go Deeper2 Go Deeper3 Plant Idea4 Escape
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Conclusion
● Common sense
● It is not about good and bad design: if you business
requires a non-normal form, it is OK
○ Normalise first, denormalisation should be used as
an optimisation
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