NormalizationNormalization: The first three formsAdditional normalization tipsNormalizationWell normalized data makes programming (relatively) easy, and works very well in multi-platform, enterprise wide environments. Non-normalized data leads to heartbreak. Normalization: The first three formsFirst Normal Form: No repeating groups. As an example, it might be tempting to make an invoice table withcolumns for the first, second, and third line item (see above). This violates the first normal form, and would result in large rows, wasted space (where an invoice had less than the maximum number of line items), and *horrible* SQL statements with a separate join for each repetition of the column. First form normalization requires you make a separate line item table, with it's own key (in this case the combination of invoice numberand line number) (See below).Second Normal Form: Each column must depend on the *entire* primary key. As an example, the customer information could be put in the line item table (see above). The trouble with that is that the customer goes with the invoice, not with each line on the invoice. Putting customer information in the line item table will cause redundant data, with it's inherant overhead and difficult modifications. Second form normalization requires you place the customer information in the invoice table (see below). Third Normal Form: Each column must depend on *directly* on the primary key. As an example, the customer address could go in the invoice table (see above), but this would cause data redundancy if several invoices were for the same customer. It would also cause an update nightmare when the customer changes his address, and would require extensive programming to insert the address every time an existing customer gets a new invoice. Third form normalization requires the customer address go in a separate customer table with its own key (customer), with only the customer identifier in the invoice table (see below).Additional normalization tipsMake a table for each list Do this right away. It will save a fortune in time. Go through the department or enterprise, ferreting out all lists. Document them. Each should be a table if their information is needed, and if practical. Use non-meaningful primary keys If employee numbers starting with C mean the person's stationed in Chicago, and the person moves to Los Angeles, what do you do with his employee number. Making primary keys non-meaningful means changes in environment or business rules can't render them
View Full Document
Unlocking...