Normalisation

  • Thread starter Thread starter Chris
  • Start date Start date
C

Chris

Hi, i'm doing AVCE double a-level at school and on the database unit. I
have to normalise the data and its really givern me bother. I am getting
there but still its quite a hard concept for my to grip. I can get past
1st NF and sort of second but i used a linking table that linked all of
my tables (4 of them) and my teacher said it cant work as there all
depenedent on each other. Well has anyone got any good links wiht
normalisation. I have books and stuff and people have tried to explain
it to me, but i jsut cant get it, im not a lamer i am good at computers,
but this is really getting on my nerves. So any down to earth
explanations would be good,

thanks
 
Chris,
go back and look at your table design. Check these six things, and you
should be on your way:

1) Each field in your tables should reflect unique information.
2) Each table should have a primary key or other unique id. - CustomerID
3) All of the fields in a table should describe the the subject of the
table, as in a Customer table - Company Name, address, city, state/province,
phone, email, fax, etc..... Not a good idea to put an Order field in
Customer table!
4) You should be able to change a field's data in any table without
affecting the data in any other field in the table (with exception of
primary keys) - in Customer table changing address info doesn't affect the
Company Name.
5) Look at the relationships between tables Compose a statement about your
tables. For instance -a Customer has many Orders... then reverse the
statement and if it doesn't fit, then you know it is one to many
relationship (an Order does not have many Customers!) If it does fit, then
it is probably a many-to-many relationship, and you will need another table
to tie the two together. As in - A warehouse location has many products,
and a product has many warehouse locations..... both true, so many to
many...
6) Link tables based on the relationships established with the foreign key
in the many side of the relationship -Customer ID as an FK in Orders table.

HTH
Damon
 
thanks mane, helped alot, I knew most of that but no ones said it like
that, seams an easier way of puttin it. i didnt really think of the way
you said in number 5, i know of M>M and O>M etc but never thought ot
like that, thanks helped alot. I will post back if i get stuck again,
Glad this dont have to be in 4th or 5th NF lol, then be really fecked

thanks
 
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