What is the difference between PRIMARY KEY and UNIQUE KEY with NOT NULL constraint?

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Hi. in data level we have: Primary key = unique identifier of a row in DB & is NOT NULL. Unique key = unique identifier of a row in DB & is NULL ABLE. in perfect design model we have: Primary key = unique identifier of an entity and is meaningless. Unique key = unique identifier of a entity and is meaningful.

Petra Zeiler19y

the primary diffrence bitween primary key & unique key is when we assign primary key to a particular column cluster index automatically created for that column.

primary key= unique +not null+ clustered index

ragi0119y

Both of them are same. we can say primary key=unique key+not null

prasad mummidi19y

What is the difference between PRIMARY KEY and UNIQUE KEY with NOT NULL constraint?

4 Answers