c# and SQL interview question :- What is the difference between uni

Description
Unique key can have nulls
Primary key cannot have nulls.

In a single table we can create multiple unique keys.In a single table we can have only one primary key.
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Unqiue key creates a non-clustered index by default.Primary Key created a clustered index by default.
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Both unique keys and primary keys can be referenced by foreign key.