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What is a functional dependency? RRS feed

  • Question

  • Hi,

         What is a functional dependcy.If functional dependcies exist ,is the table in 2nd normal form ?

     

      

    Tuesday, May 17, 2011 5:45 AM

Answers

  • Functional Dependencies are fundamental to the process of Normalization Functional Dependency describes the relationship between attributes(columns) in a table.

    For example, if A and B are attributes of a table, B is functionally dependent on A, if each value of A is associated with exactly one value of B (so, you can say, 'A functionally determines B').

    Have a read of http://www.mahipalreddy.com/dbdesign/dbqa.htm

     


    Jeff Wharton MSysDev (C.Sturt), MDbDsgnMgt (C.Sturt) MCT, MCPD, MCITP, MCDBA, MCSD, MCAD
    Tuesday, May 17, 2011 6:11 AM

All replies

  • There is first/second/third... normal form, each one has its requirements

    http://en.wikipedia.org/wiki/Second_normal_form

    http://en.wikipedia.org/wiki/Functional_dependency


    Best Regards, Uri Dimant SQL Server MVP http://dimantdatabasesolutions.blogspot.com/ http://sqlblog.com/blogs/uri_dimant/
    Tuesday, May 17, 2011 5:52 AM
  • Hi,

             2nd NF and 3rd NF has something to do with Functional dependencies,i got it.But ,What functional dependecy has to do with First normal .1 Nf say

    Attributes should have only one value.So,what kind of Functional dependencies exist in 1NF?

     

    regards

    Chaithu

           

     

       

    Tuesday, May 17, 2011 6:00 AM
  • Functional Dependencies are fundamental to the process of Normalization Functional Dependency describes the relationship between attributes(columns) in a table.

    For example, if A and B are attributes of a table, B is functionally dependent on A, if each value of A is associated with exactly one value of B (so, you can say, 'A functionally determines B').

    Have a read of http://www.mahipalreddy.com/dbdesign/dbqa.htm

     


    Jeff Wharton MSysDev (C.Sturt), MDbDsgnMgt (C.Sturt) MCT, MCPD, MCITP, MCDBA, MCSD, MCAD
    Tuesday, May 17, 2011 6:11 AM
  • I do not think that functional dependecy has to do with First normal form
    Best Regards, Uri Dimant SQL Server MVP http://dimantdatabasesolutions.blogspot.com/ http://sqlblog.com/blogs/uri_dimant/
    Tuesday, May 17, 2011 6:28 AM
  • I do not think that functional dependecy has to do with First normal form
    Best Regards, Uri Dimant SQL Server MVP http://dimantdatabasesolutions.blogspot.com/ http://sqlblog.com/blogs/uri_dimant/

    That is correct
    Jeff Wharton MSysDev (C.Sturt), MDbDsgnMgt (C.Sturt) MCT, MCPD, MCITP, MCDBA, MCSD, MCAD
    Tuesday, May 17, 2011 6:30 AM
  • Yes, Functional Dependency is related to 2NF, which says "For a relation to be in 2NF its all non-key attributes should be functionally dependent on the entire primary/candidate key." Check this blog link for more on Normalization & its 3 NFs.


    ~manoj | email: http://scr.im/m22g
    http://sqlwithmanoj.wordpress.com
    MCCA 2011
    Saturday, May 21, 2011 8:51 AM