What is the difference between unique and primary key?

Question

In SQL

Answer 1

in unique constraint , u can have null values ... but in primary u can't have null values
//duplicate values is not allowed in both
https://stackoverflow.com/questions/9565996/difference-between-primary-key-and-unique-key

Answer 2

An unique constraint on an attribute would allow null values (albeit only one). An attribute which is designated as primary key is both unique and not null.

Answer 3

You Get Everything from here: https://www.essentialsql.com/primary-and-unique-key/

Answer 4

thank you for the ans