A Unique ID and Primary Key Constrain perform the ability to allow unique data in the column but only the Unique constrain allows NULL values in the field along with the unique data. Primary Key constrain fields allow Unique and Not NULL values.
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sunil neha juhi singh
Answered On : Jun 28th, 2012
primary key=not allow null values,create cluster index by default.
unique key=allow only one null values and by default it create non cluster index
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