Fellow Monks,

I have been playing with the handy Geo::Distance module, however I noticed some abnormalities using the 'closest' function for certain lat/lon data when doing DB lookups...

I couldn't work out why this was wrong and looked a bit further, simply put this 'closest' function creates some simple sql to fine destinations within a certain range of lat/lon

However I noticed this info was wrong, however when I did the same sql directly on the DB it did what I expected. Further testing showed that it was only incorrect when placeholders were used, and I think its related to using negative numbers in the logic. Take a look at the following code snippet


y $lon = -0.232323127347249;
my $sql = qq| SELECT lon,lat,location_id
                FROM lat_long
                WHERE lon>= $lon|;

my $sth = $sp->dbh->prepare($sql);
$sth->execute();
print STDERR "Rows not using placeholders ".$sth->rows."\n";
$sql = qq| SELECT lon,lat,location_id
                FROM lat_long
                WHERE lon >= ?|;
$sth = $sp->dbh->prepare($sql);
$sth->execute($lon);
print STDERR "Rows using placeholders ".$sth->rows."\n";

[download]

I would have expected that the 2 SQL would return exactly the same number of results but it doesn't !! see below

Rows not using placeholders 5488
Rows using placeholders 12888

[download]

Maybe I am missing something obvious but I do not see how this could happen ? any ideas how to debug further ?

Update : Adding some sample data

__DATA__
insert into lat_long (location_id, lat, lon) values(44977, 48.3547, 11
+.7875);
insert into lat_long (location_id, lat, lon) values(53280, 48.1369, 11
+.5456);
insert into lat_long (location_id, lat, lon) values(53281, 48.1394, 11
+.5454);
insert into lat_long (location_id, lat, lon) values(53282, 47.6869, 11
+.7609);
insert into lat_long (location_id, lat, lon) values(53283, 48.3547, 11
+.7875);
insert into lat_long (location_id, lat, lon) values(60105, 48.3547, 11
+.7875);
insert into lat_long (location_id, lat, lon) values(80766, 48.3507, 11
+.7328);
insert into lat_long (location_id, lat, lon) values(71776, 48.1435, 11
+.5574);
insert into lat_long (location_id, lat, lon) values(65883, 48.1269, 11
+.6363);
insert into lat_long (location_id, lat, lon) values(65884, 48.1515, 11
+.6178);

[download]

In reply to Placeholders and Negative Numbers.. by ropey

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