Distance between Long Lat coord using SQLITE

Question

I've got an sqlite db with long and lat of shops and I want to find out the closest 5 shops.

So the following code works fine.

    if(sqlite3_prepare_v2(db, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {


    while (sqlite3_step(compiledStatement) == SQLITE_ROW) {

        NSString *branchStr = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 0)];
        NSNumber *fLat = [NSNumber numberWithFloat:(float)sqlite3_column_double(compiledStatement, 1)];
        NSNumber *fLong = [NSNumber numberWithFloat:(float)sqlite3_column_double(compiledStatement, 2)];

        NSLog(@"Address %@, Lat = %@, Long = %@", branchStr, fLat, fLong);
        CLLocation *location1 = [[CLLocation alloc] initWithLatitude:currentLocation.coordinate.latitude longitude:currentLocation.coordinate.longitude];
        CLLocation *location2 = [[CLLocation alloc] initWithLatitude:[fLat floatValue] longitude:[fLong floatValue]];

        NSLog(@"Distance i meters: %f", [location1 getDistanceFrom:location2]);
        [location1 release];
        [location2 release];
    }       
}

I know the distance from where I am to each shop. My question is.

1. Is it better to put the distance back into the sqlite row, I have the row when I step thru the database. How do I do that? Do I use the UPDATE statement? Does someone have a piece of code to help me.

2. I can read the sqlite into an array and then sort the array. Do you recommend this over the above approach? Is this more efficient?

Finally, if someone has a better way to get the closest 5 shops, love to hear it.

Answer 1

The fastest way to find nearby locations in SQL is to use the Haversine formula in an SQL query. Do a Google search for sqlite and Haversine and you'll find an implementation.

Here's one I've used before:

http://www.thismuchiknow.co.uk/?p=71