After I told these two articles, what might be the difference between the two of them. You can find the differences below.
- Primary Key can not contain null value
- A table can only have one primary key.
- Sparse columns can not be used as part of the primary key.
- By default, when you set a column as a primary key, that column is created as a clustered index, and the table is physically sorted according to this column (you can browse the Clustered Index and Non Clustered Index Differences named nomenclature).
- Primary Key can be associated with another table Foreing Key.
- Self-incrementing identity can be set.
- It can contain 1 Null value. Because 2nd Null value corrupts singularity. You will get an error like the following.
Violation of Unique Key Constraint ‘x’. Cannot insert duplicate key in object ‘x’.
- Each table can have more than one Unique Constraint
- By default, if you put a unique constraint on a column, a nonclustered index created on that column.
- Self-incrementing identity can not be set.