What's the difference between a primary key and a unique key?
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What's the difference between a primary key and a unique key?
by Micheal Tue Jan 12, 2010 8:38 pm
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.
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.
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