How to calculate distance between two zipcode?

To calculate the distance between two zipcode, you need a table which stores latitude and longitude for all the cities.

CREATE TABLE `zip_codes` (
  `zip` varchar(5) NOT NULL default '',
  `state` char(2) NOT NULL default '',
  `latitude` varchar(10) NOT NULL default '',
  `longitude` varchar(10) NOT NULL default '',
  `city` varchar(50) default NULL,
  `full_state` varchar(50) default NULL,
  UNIQUE KEY `zip` (`zip`)
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

INSERT INTO `zip_codes` VALUES ('35004', 'AL', ' 33.606379', ' -86.50249', 'Moody', 'Alabama');

You can use the below logic to calculate the distance:-

import java.lang.Math;
import java.lang.Double;

public int calcDistance(double latA, double longA, double latB, double longB)
{
  double theDistance = (Math.sin(Math.toRadians(latA)) *
                        Math.sin(Math.toRadians(latB)) +
                        Math.cos(Math.toRadians(latA)) *
                        Math.cos(Math.toRadians(latB)) *
                        Math.cos(Math.toRadians(longA - longB)));

  return = (Math.toDegrees(Math.acos(theDistance))) * 69.09;
}

SQL script to setup zipcode table - http://zips.sourceforge.net/