On Thursday, 28. June 2001 06:44, Christian Anton wrote:
> Hello all,
>
> I am fairly new at db design, I have built a few simple in the past
> and have never dealt with this type of problem before, any help would
> be appreciated.
>
> I have three attributes in one table that should reference one, and
> only one, attribute in another table. Here's an analogy of the
> problem:
>
> I have a table with a list of marbles, each marble has three colors
> in it (color1, color2, color3) and a serial number. In another table
> I have eight colors to choose from but the list of colors grows
> regularly. How do I associate a marble with three colors from the
> color table (a marble may have three red sides or red-yellow-blue)?
Quite easy:
-- The list of colors. id is a automatically assigned unique number.
-- You could use INT4 instead of SERIAL and make numbers of your own.
CREATE TABLE color (id SERIAL PRIMARY KEY,name text
);
-- The list of marbles. The colors reference to the table color.
-- Postgres makes sure that only existing colors are entered.
CREATE TABLE marble (number SERIAL PRIMARY KEY,color1 int4 REFERENCES color,color2 int4 REFERENCES
color,color3 int4 REFERENCES color
);
-- But you want to see the color's name rather its id, isn't it?
CREATE VIEW v_marble ASSELECT m.number, c1.name as color1, c2.name as color2, c3.name as color3FROM marble m, color c1,
colorc2, color c3WHERE m.color1 = c1.id AND m.color2 = c2.id AND m.color3 = c3.id;
Hope that helps.
Christof
-- gl.aser . software engineering . internet service http://gl.aser.de/ . Planckstraße 7 . D-39104
Magdeburg
Tel. +49.391.7 44 77 10 . Fax +49.391.7 44 77 13 . Mobil 0177.77 92 84 3