What is Unique Constraint in SQL Server - SQL Server / TSQL Tutorial Part 95

SQL Server / TSQL Tutorial Scenario:
What is Unique Constraint in SQL Server:

Unique Constraint in SQL Server is created on a column or columns to restrict the column/s to accept only unique values.
Only single Null value is allowed in a column on which Unique Constraint is created.

Scenario:

Let's say that you are working as SQL Server developer for insurance company, you are asked to create dbo.Customer table that should have a column SSN and it should always accept Unique values.

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