If you visualise your search area as a circle around your 'target' coordinates, then you can eliminate many of the irrelevant rows by search for coordinates that fall within a square surrounding that circle.
So, imagine a simple grid with target coordinates of 6,8 and a search radius of 3. Therefore you search WHERE x BETWEEN 3 AND 9 AND y BETWEEN 5 AND 11. I'm not certain but I think MySQL should be able to used a combined index of (x,y) for that. As you probably know you can use EXPLAIN SELECT to check whether MySQL is using an index. HTH, James Harvard At 12:01 pm +0000 10/1/06, Ben Clewett wrote: >I have a need to locate (x,y) coordinates from mysql where they are close to >another coordinate. For instance, all pizza bars near my car. > >Example: Searching for points closer than z to (i,j) using Pythagoras: > >SET i = 10; >SET j = 10; >SET z = 30; >SELECT x, y > FROM coordinates > WHERE POW(x - @i, 2) + POW(y - @i, 2) < POW(@z, 2) > >Big problem! Must searches every row. Linear indexing not able to help here. -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
