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primary_set_relational_primary_key_.htm
Navigation:  Language Reference > 5 - Declaration Attributes > Variable and Entity Attributes >====== PRIMARY (set relational primary key) ====== Previous pageReturn to chapter overviewNext page

PRIMARY

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The PRIMARY attribute (PROP:PRIMARY) specifies the KEY is unique, includes all records in the file, and does not allow “null” values in any of the fields comprising the KEY. This is the definition of a file's “Primary Key” per the relational database theory as expressed by E. F. Codd.

Example:

Names   FILE,DRIVER('TopSpeed'),PRE(Nam)   !Declare a file structure

NameKey   KEY(Nam:Name),OPT                !Declare name key, exclude blanks

NbrKey    KEY(Nam:Number),PRIMARY            !Declare number key as the primary key

Rec        RECORD

Name        STRING(20)

Number      SHORT

          END

      END

See Also:

KEY

primary_set_relational_primary_key_.htm.txt · Last modified: 2021/04/15 15:57 (external edit)