sql server - constraints
TRANSCRIPT
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Constraints
Presentation by Aaron BumaDev Lead and DBA
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Session Overview
•Constraints
•Data Integrity
•Demos
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Primary Key Constraint
•Most common constraint
•Doesn’t allow NULL or duplicates
•There can only be one per table
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Unique Constraint
•Can be used when a table already has a Primary Key
•Does not allow duplicates, but DOES allow a NULL
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Check Constraint
•Enforces domain integrity, data must conform
•Can refer to a single or multiple columns
•Example: column value must be > 3.
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Default Constraint
•Useful for inserting data into “NOT NULL” columns
•Can be dynamic, example: Using GETDATE()
•Can be overridden with actual values
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Foreign Key Constraint
•A value in the FK’d table exists as a Primary Key of a table, usually a different one
•Verifies constraint on EXISTING data and NEW data– “WITH NOCHECK” only verifies NEW data
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Data Integrity
•Domain Integrity (Constraint on individual value)– Check Constraints
•Entity Integrity (Looks at entire table)– Primary Keys, Unique Constraints
•Referential Integrity (must exist in other table)– Foreign Keys
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DEMOS
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Review
• Constraints
• Data Integrity
Presentation Recording, Slides and Scripts– Available at: http://www.AaronBuma.com