[Courses] [Postgresql] Week 5: Even More SQL

[Matthias Urlichs]

Hi,

Julie Pichon:
> I was wondering if anyone could provide an example where a CROSS JOIN
> would be useful?

Let's say I have a table of zip codes (and their geo coordinates). I
want to pre-populate a table of distances so that I can use that for
fast sorting of users-who-have-nothing-interesting-in-common in my
matchmaking database. ;-)

I do

	select z1.zip,z2.zip,z1.geo,z2.geo from ziplist z1, ziplist z2 \
		where z1.zipcode < z2.zipcode;

and proceed from there.

-- 
Matthias Urlichs   |   {M:U} IT Design @ m-u-it.de   |  smurf at smurf.noris.de
Disclaimer: The quote was selected randomly. Really. | http://smurf.noris.de
 - -
Nearly every complex solution to a programming problem that I
have looked at carefully has turned out to be wrong.
		-- Brent Welch