SQL Unique key with Example

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Unique Key

Unique key is similar to primary key and does not allow duplicate values in the column. It has below differences in comparison of primary key:

  1. it allows one null value in the column.
  2. by default, it creates a nonclustered index on heap tables.

The unique key can be defined as a set of one or more fields/columns of a table that have the capability to uniquely identify a record in the database table.

We can have other fields also in a table beyond primary key which is also able to uniquely identify the record. It can accept only one null value and it cannot have duplicate values in it.


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