What is a unique key?

<p>A <strong>Unique key</strong> constraint uniquely identified each record in the database. This provides uniqueness for the column or set of columns.</p> <p>A <strong>Primary key</strong> constraint has automatic unique constraint defined on it. But not, in the case of Unique Key.</p> <p>There can be many unique constraint defined per table, but only one Primary key constraint defined per table.</p>