ER Model, Keys and Integrity Constraints Short Notes for GATE DA: Concepts, Formulas, Worked Examples & Practice

    ER Model, Keys and Integrity Constraints short notes for GATE DA: 2 study cards covering concepts, formulas, shortcuts and exam traps, plus solved practice questions.

    Summary: Mapping Rules Cheat Sheet

    Summary: Mapping Rules Cheat Sheet

    Entity / Relationship Type Mapping Rule
    Strong EntityRelation with same name. PK becomes PK.
    Weak EntityRelation. Owner PK becomes FK. Owner PK + Discriminator = PK.
    1:N RelationshipOwner PK becomes FK in the N-side relation.
    M:N RelationshipNew relation. PK is union of both entity PKs.
    1:1 RelationshipOne PK becomes FK in the other relation. Place in the totally participating side.
    Multivalued AttrNew relation. Entity PK + Attribute. PK is both.
    n-ary RelationshipNew relation. PK is union of all participating entity PKs.

    Quick Recall: Keys, NULLs, and FKs

    Final Cheat Sheet

    NULL Logic

    • NULL = NULL is Unknown (not True).
    • Use IS NULL to check for NULLs.

    Key Constraints

    • Primary Key: Must be UNIQUE and NOT NULL.
    • Unique Key: Must be UNIQUE. Allows NULLs (multiple NULLs permitted in standard relational model).

    Referential Integrity (Foreign Keys)

    • FK value must exist in Parent PK OR be NULL.
    • Safe Operations (Never Violate): Insert Parent, Delete Child, Update non-keys.
    • Risky Operations (Can Violate): Insert Child (if FK invalid), Delete Parent (if referenced).

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    ER Model, Keys and Integrity Constraints Short Notes for GATE DA: Concepts, Formulas, Worked Examples & Practice

    ER Model, Keys and Integrity Constraints short notes for GATE DA: 2 study cards covering concepts, formulas, shortcuts and exam traps, plus solved practice qu

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