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Old 01-30-2017, 05:07 AM   #1
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Join Date: Jun 2015
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Arrow What's the difference between a primary key and a unique key in SQL?

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 does not allow NULLs, but unique key allows one NULL only.

Asthi jivak | Fat Cutter
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