Database normalization design - single or multiple tables

Question

Should this be represented in the database as 1 table or 3 tables? I and my friend have different opinions about this so I\'d like to see the general views on this. (Maybe

Answer 1

If you want to avoid data duplication, you should go with a 2- or 3-table solution. For example, if you have the External columns in the Order table, value could exist multiple times. If the data looks like this:

ID   ExternalCompanyName
1    ACME
2    ACME
3    My Company
4    ACME

Now, if ACME changes names to ACME, Inc. you must update many rows. If the tables are normalized, where external companies are in a separate table, you would update one row. Note, there may be an argument to put Account Number in it's own table, but we'll leave that for extreme normalization.

It doesn't appear to be a 1-to-1 relationship between an order and a company/account, unless each company/account can only have one order. it sounds more like a 1-to-many relationship.

Now, what happens if a mistake is made when updating the ExternalCompanyName in a single-table environment, and only some of the rows get updated. You have some rows with ACME and some rows with ACME, Inc. You end up with a bad-data situation.

Also, if this is really a 1-to-many relationship, you really aren't saving space. You are duplicating data in the order, rather than storing it once in another table.