SMG IS 465 Lecture Notes - Lecture 5: Mathematical Object, Multivalue, Unique Key

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A relation loosely corresponds to a 2-d table of data. Its a mathematical object that meets addtl requirements. Every attribute value must be atomic (not multivalued, not composite) Every row must be unique in value. The order of the columns must be irrelevant. The order of the rows must be irrelevant. Keys are special fields used to uniquely identify instances. Primary keys are unique identifies of the entity in question. Foreign keys can only refer to other primary keys. Keys are often used with indexes to speed up user queries. Foreign key value must match a primary key value in another table or be null. When a referenced record from parent table is deleted. Restrict: dont allow delete of parent primary side if related rows exist in dependent/foreign side. Cascade: automatically delete dependent/foreign side rows that depend on the deleted parent/primary row. Set-to-null: set the foreign key in the dependent side to null if deleting from the parent side.

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