Difference between primary key and unique key ?

Answer Posted / lucky

Primary key not accepts to null values in database, but
uniqe key accepts to the null values in database.

Each table having only one PRIMARY KEY.And my contain many
UNIQUE KEYS.
PRIMARY KEY is identity of each row. UNIQUE KEY also
identity of each row.
BOTH keys will not contain repeated value.
BUT UNIQUE KEY will contain NULL value but PRIMAY key will
not contain NULL value.

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