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difference..between PK and UK

  • April 10, 2006 at 11:11 am

    #91625

    I was asked this question..what is the difference...in one table a column is primary key..and in another table a column is unique key and not null..i said the second option is equivalent to primary key..Am i right?

    thks

  • April 10, 2006 at 11:30 am

    #631797

    They both ensure that no duplicate values can be entered into a column (or set of columns), but there are differences in how they should be used.  See UNIQUE Constraints in BOL.

    John Rowan

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  • April 11, 2006 at 8:26 am

    #631935

    Designating the column as Primary Key causes it to be used as the base lookup of any indexes that are applied to the table (by default it is also clustered, if you do not specify otherwise).

  • April 11, 2006 at 12:51 pm

    #631955

    Certain facilities (such as full text indexes) require there to be a primary key on a table.

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