Term: UNIQUE

Definition:
The UNIQUE constraint ensures that all values in a column are distinct, that is, the column cannot contain two identical instances of any value. Attempting to insert a duplicate value into a UNIQUE column will violate the UNIQUE constraint and result in an error.

The UNIQUE and PRIMARY KEY constraints both provide a guarantee for uniqueness for a column or set of columns.

Note that a PRIMARY KEY constraint automatically includes a UNIQUE constraint.

Example Syntax:

CREATE TABLE users

(user_id integer Unique,

Last_Name varchar (30),

First_Name varchar(30));

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