What’s the difference between a primary key and a unique key?

Technology CommunityCategory: DatabasesWhat’s the difference between a primary key and a unique key?
VietMX Staff asked 1 year ago

Both primary key and unique key enforces uniqueness of the column on which they are defined.

But by default primary key creates a clustered index on the column, where are unique creates a non-clustered index by default.

Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only.