Wipro Interview Question:

Can you please explain the difference between unique and primary key constraints?

Submitted by: Muhammad

A UNIQUE constraint is similar to PRIMARY key, but you can have more than one UNIQUE constraint per table. Contrary to PRIMARY key UNIQUE constraints can accept NULL but just once. If the constraint is defined in a combination of fields, then every field can accept NULL and can have some values on them, as long as the combination values is unique.
Submitted by: Muhammad