What is the difference between unique and primary key constraint?

What is the difference between unique key and primary key constraints?

Primary key will not accept NULL values whereas Unique key can accept NULL values. A table can have only one primary key whereas there can be multiple unique key on a table. A Clustered index automatically created when a primary key is defined whereas Unique key generates the non-clustered index.

What is the difference between unique and primary?

Both Primary key and Unique Key are used to uniquely define of a row in a table. Primary Key creates a clustered index of the column whereas a Unique creates an unclustered index of the column . A Primary Key doesn't allow NULL value , however a Unique Key does allow one NULL value .

What is difference between unique and primary key constraint co1?

primary key is always unique and not null. but unique key is only unique it can be null. "UNIQUE constraints allow for the value NULL. However, as with any value participating in a UNIQUE constraint, only one null value is allowed per column."