DEFINE PRIMARY AND UNIQUE KEY.

Amit Singh

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  1. Amit Singh

    Post:565

    Points:2825
    Define Primary and Unique key.

    Primary Key

    • The column or columns of the table whose value uniquely identifies each row in the table is called primary key.
    • You can define column as primary key using primary key constraint while you create table.
    • When you define a column as primary key, a unique index is created which restricts duplicate data and fast access to data.
    • A column defined as primary key doesn’t allow null value.
    • By default, clustered index in created with the column having primary key.

    Unique key

    • Unique key also ensures data uniqueness like primary key.
    • A column with unique key defined allows null value.
    • By default, it creates non-clustered index.

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