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  • Primary Key

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    Primary Key

    A primary key in a table is a unique key that is the element in this column are unique and can not be null.

    It is used to mantain the integrity.

    It uniquely identify the row in the table.

    It is a constraint on the table.

    It can not have more than 16 columns.

    It can also be a group of columns.

           ID   INT              NOT NULL,
           NAME VARCHAR (20)     NOT NULL,
           AGE  INT              NOT NULL,
           ADDRESS  CHAR (25) ,
           SALARY   DECIMAL (18, 2),       
           PRIMARY KEY (ID)

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