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Hi Kate,
Both primary key and unique key enforce uniqueness of the column on which they are defined. But by default, the primary key creates a clustered index on the column, whereas unique key 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.
Nimol
Programmer
Corbin Creative Databases, LLC
http://www.corbincreative.com
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