What’s the difference between a primary key and a unique key?
By admin on Mar 14, 2007 in Ms Sql Server Interview Questions
Both primary key and unique enforce 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 nonclustered index by default. Another major difference is that, primary key doesn’t allow NULLs, but unique key allows one NULL only.
