From: "Dan Haley" <[EMAIL PROTECTED]>
>
> 2. make sure to join the two tables using primary/foriegn key (parent/child)
> relationships, otherwise you get a cartesian join (and, no, I don't really
> know what that means either, you just get all the records from both tables)
>
cartesian
>From Rene Descartes ...
in cartesian coordinates there is an abscissa and an ordinate,
respectively the measurement of distance from an origin
of an orthognal line projected from the coordinate point
to the appropriate axis. In simple two dimensional cartesian
systems based on a plane there is a y (ordinate) value for
every x (abscissa) value. This is commutative; i.e. for every
y there is a x. Thus, each coordinated point has, at least,
two ordered pairs of numbers (or addresses) that, while
identically referencing unique points, are distinct.
A cartesian join supplies an answer to each iteration of both
of the questions, 1. what value y is at each x AND 2. what
value x is at each y. Thus you get a recordset that fills an
entire quadrant of possible points comprised of both the
ordered pair (x,y) and the complementary ordered pair
(y,x). You know that (x,y) == (y,x) but your query doesn't.
Queries produce rows - so you get
x0 - value y0
x1 - y1
...
xn - yn
[and then,]
y0 - value x0
y1 - x1
yn - xn
By writing the appropriate sql you avoid this (or produce it
if your goal is a cartesian join) and get a recordset that
comprises just the (x,y) coordinations or the (y,x)
coordinations - your choice.
This can be made much more complicated if desired.
Pan - "Or, something close to that" - Az M'Tope
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