Primary and Unique Key

Difference between Primary key and Unique Key
No. Primary Key Unique Key
1 Can be only one in a table Can be more than one unique key in one table.
2 It never allows null values Unique key can have null values
3 Primary Key is unique key identifier and can not be null and must be unique. It can’t be candidate key
4 Unique key can be null and may not be unique.
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