difference between primary key and Unique key

• surya prakash

  SSC-Addicted

  Points: 455

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  October 11, 2004 at 3:20 am

  #83854

  Hi,

  I have come across interview microsoft. I have been asked for the difference between primary key and unique key.

  I have given answer that Unique key allows one null where as primary key wont allow nulls.

  the interviewer asked if i made unique key along with not null they is that equals to primary key??

  What should be the answer. Please reply me.

   

• wsplinter

  SSC Enthusiast

  Points: 129

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  October 11, 2004 at 4:07 am

  #526110

  The answer is a unique key creates a nonclustered index by default

• MVDBA (Mike Vessey)

  SSC-Insane

  Points: 21797

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  October 11, 2004 at 6:27 am

  #526128

  what about referential integrity - primary key foreign key relationships.

  if you build these relationships on unique indexes (not keys) then products like MSACCESS would not be able to update queries where there is a join.

  MVDBA