On 18 Oct 2005 08:03:59 -0700,
wa********@yahoo.com wrote:
If you have several entities that have many common properties but a few
have a few unique fields to them how do you design your tables?
DO you make a seperate table for each entity even though they have many
common fields or is there a way to do an OO type thing where you have a
common table for all and somehow tack on the unique fields?
Just unsure whats possible and what's best.
Thanks for any input.
The standard way I've always seen and often do is to have a "base" table with
the common fields, and a 1-to-1 relationship to tables with fields for the
specific case. There's even a symbol for this used on database diagrams.
Here's an example
address
address_id
country
country_subdivision
city
postal_code
street_address
address_id
street_name
street_number
postal_address
address_id
postal_box
Every address has an "address", and every address will have either a
"street_address" or a "postal_address", but not both.