gcheers

Hi, I\'m developing a personals site whereby users can search profiles using zip codes. One of the most important features of this site will be the ability to search for profiles within a certain mile radius of a zip code. e.g. I am an x looking for a y within a z mile radius of \'A\' (where A is the searchers ZIP CODE) I have a zip code database which consists of 42,000 rows each entry has CITY,ZIPCODE,AREACODE,STATENAME,LATITUDE,LONGITUDE,COUNTYNAME Rather than put a huge stress on the server by calculating distances between A and B on the fly, I thought I would create a matrix whereby each unique zip code would be cross-referenced with every other unique zip code. A distance in miles (as the crow flies) would be calculated using PHP (Long,Lat) and inserted for each unique combination of 2 zip codes. So, TABLE would resemble something like. ZIP1,ZIP2,30 ZIP1,ZIP3,47 ZIP1,ZIP4,47 ZIP2,ZIP3,17 ZIP2,ZIP4,50 ZIP3,ZIP4,32 IF I have 42,000 unique zip codes, 1. How many rows will I end up with (approximately)? 2. Is this the best approach? I envisaged that queries where: ZIP1=\'A\' AND DISTANCE<z would work quite well? Any input greatly appreciated. PS. (I\'m in the UK, dont know much about zip codes, are there really 42,000 or do I have too many!?)