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What's the difference between a primary key and a unique
key?
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Answer Posted / swapna
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.
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