design question

When or why does one make the decision to create a table instead of just 
entering the data. Example ..... zip codes or this day in age phones. 
Home phone, work phone, cell phone 1, cell phone2 ..... Create a phone 

Hi,

This is called normalization. Imagine a table with Persons and their
Addresses. If you just create separate columns HomePhone, WorkPhone,
CellPhone1, CellPhone2 you will certainly come to a point where
somebody does have three cell phones. Where to store that then? Always
creating new columns is a design you would apply for a Spreadsheet but
a database has a totally different concept. You would also run into a
complete nightmare when you try to query such spreadsheet design
data.

You would be better if you create a separate table PhoneNumbers and
have columns like PhoneType and PhoneNumber.

Zip codes might not require a separate table if you just want to store
one by address, but as you did not gave more specs it is difficult to
comment on this.

brgds

Philipp Post