runeveryday Posted September 3, 2009 Share Posted September 3, 2009 StudyNo | Name | Sex | Email | ClassNo | ClassAddress 01 john Male kkkk@ee.net 200401 A building 1 02 mary famale kkk@fff.net 200402 A building 2 the above is a table. StudyNo is the primary key,a friend of mine said the above is fit for the first normal form,but doesn't fit for the second.the reason is "ClassAddress" partial dependencies on the key ClassAddress, why?who can explain it to me! thanks very much. Quote Link to comment Share on other sites More sharing options...
kickstart Posted September 3, 2009 Share Posted September 3, 2009 Hi Which of those fields depend entirely on the primary key? Can a person have multiple StudyNo, multiple ClassNo, multiple ClassAddress? All the best Keith Quote Link to comment Share on other sites More sharing options...
runeveryday Posted September 3, 2009 Author Share Posted September 3, 2009 i can't understand. table1: StudyNo | Name | Sex | Email | ClassNo 01 john Male kkkk@ee.net 200401 02 mary famale kkk@fff.net 200402 table2: ClassNo | ClassAddress 200401 Abuilding1 200402 Abuilding2 are fit for the second NF,the primary key is StudyNo ,ClassNo why the first doesn't fit for the second NF Quote Link to comment Share on other sites More sharing options...
kickstart Posted September 3, 2009 Share Posted September 3, 2009 Hi Can each person only be in a single ClassNo, and does a person on have a single StudyNo? If so then it would appear splitting it into 2 tables has resulted in it being normalised. Duplicates have been removed (first normal form), all fields are dependent on the primary key (2nd normal form) and nothing is dependent on anything other than the primary key (3rd normal form) Check the link on the thread on normalisation to the MySQL site:- http://dev.mysql.com/tech-resources/articles/intro-to-normalization.html All the best Keith Quote Link to comment Share on other sites More sharing options...
runeveryday Posted September 3, 2009 Author Share Posted September 3, 2009 Thanks a Lot for spending time with my questions. But it would be helpful for me,if u explain the first ,second,third normal form with some simple examples here....so that I can understand it very clearly................ Quote Link to comment Share on other sites More sharing options...
kickstart Posted September 3, 2009 Share Posted September 3, 2009 Hi Afraid I am not good at explanations like that. The link to the MySQL site explains it far better than I can. All the best Keith Quote Link to comment Share on other sites More sharing options...
fenway Posted September 8, 2009 Share Posted September 8, 2009 Normal forms are evil and complicated to explain. If any information is duplicated across rows or columns, then it's not normal enough -- start with that. Quote Link to comment Share on other sites More sharing options...
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