Addresses should definitely have their own table.
Have you considered using Postgres? It allows for table inheritance in much the same way that inheritance works in OOP. You could have a parent table (like a parent class) for "People", and child tables (just like child classes) for "Employee", "non-Customer", and "Customer". This is the preferred approach, but few other RDMBS solutions support this (or much SQL 99 at all).
If you're not using Postgres, another way to do this would be to create a many-to-many relationship between your "People" tables, so that an address ID is related to a person ID.
Visio balks at using a non-unique foreign key because this is bad design. A "key" must be unique by nature, and indexing is much faster the column is guaranteed to have unique values. If you go with your original approach, make a combined key on both the type and foreign key fields.
Hope this helps,
Jeremy
Tony Yau wrote:
Hi Tony, Miguel
yes that was my intention at first, but to absorb all three, Shop, Employee, and Customer (and there may be 2 more to come) into an Address table would be inefficient both in storage space and search time,..no?
having this compound keys at a separate Address table is essentially the same idea, but I know it doesn't 'feel' right, for a start in Visio I can't put a link to the Address table (because fkey can't be a foreign key to both Shop and Employee)!!!
Apart from that, the tables are efficient, searching would be much quicker for non-address info.
Tony
"Tony S. Wu" <tonyswu@xxxxxxx> wrote in message news:c294d647ad3c9be9aa3c37b9ccf98df4@xxxxxxxxxx
actually, no, Shop, Employee, and Customer are not distinct. in your instance they are the same type of entry. don't distinguish them by tables, rather use a column to hold some sort of an ID for each type. of course you'll end up with a table with many columns, and many of them will be null depending on which type an entry is. but with this approach, you can easily associate with an address table.
Tony S. Wu tonyswu@xxxxxxx
On May 14, 2005, at 4:49 AM, tony yau wrote:
Hi Miguel, Thanks for the reply.
the non-customer is actually a Shop, so Employee, Customer and Shop are distinct enough to have their own tables. Now they all have an Address, and the problem is how do I allow multiple addresses for each these 'people' (without using a lookup table)
tony.
"Miguel Guirao" <miguel.guirao@xxxxxxxxxxxxxxx> wrote in message news:GFEHIFBDMNHCPDFHEJDGEEOOCDAA.miguel.guirao@xxxxxxxxxxxxxxxxxx
The schema of your table is wrong, is you do bnormalize it you will find
out
that you need two tables for this approach.
One table for your people and another one for the n addresses of your people.
If you keep your current schema, you will have as many rows for one person as many addresses for that person you have, and you will be duplicating
many
fields. So you must split your tables, one for your people and another for your people's addresses.
-----Original Message----- From: tony yau [mailto:tony.yau@xxxxxxxxxxxx] Sent: Viernes, 13 de Mayo de 2005 09:27 a.m. To: php-db@xxxxxxxxxxxxx Subject: novice on table design
Hi all,
I have the following tables
Employee Customer non-Customer
Address
========== ========== ============= ========== pkey pkey pkey pkey number type type ... payrate grant capital
I need to allow the three types of people to have n addresses, so I've
added
a type to distinguish the 3 types of people and their respective pkey onto address table.
Address ========= pkey ... type (either Employee, Customer or non-Customer etc) fkey (the pkey of Employee, Customer or non-Customer etc)
I know this design looks awkward but it does have the advantage of having less tables otherwise. BUT somehow it doesn't feel right. Can someone points me its pros and
cons.
thanks all. Tony Yau
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