slower query for searching nearby coordinates - mysql

Question

I seem to hit slower query result for searching nearby coordinates ( for now the query is for latitude). This is a mysql query
select ABS(propertyCoordinatesLat - 3.33234) as diff from tablename order by diff asc limit 0,20
is there a way to improve this besides relying on server scripting to do the sorting?
table dump.
CREATE TABLE `property` (
`propertyID` bigint(20) NOT NULL,
`propertyName` varchar(100) NOT NULL,
`propertyCoordinatesLat` varchar(100) NOT NULL,
`propertyCoordinatesLng` varchar(100) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
--
-- Indexes for dumped tables
--
--
-- Indexes for table `property`
--
ALTER TABLE `property`
ADD PRIMARY KEY (`propertyID`),
ADD KEY `propertyCoordinatesLat` (`propertyCoordinatesLat`,`propertyCoordinatesLng`),
ADD KEY `propertyCoordinatesLat_2` (`propertyCoordinatesLat`),
ADD KEY `propertyCoordinatesLng` (`propertyCoordinatesLng`);
--
-- AUTO_INCREMENT for dumped tables
--
--
-- AUTO_INCREMENT for table `property`
--
ALTER TABLE `property`
MODIFY `propertyID` bigint(20) NOT NULL AUTO_INCREMENT;
COMMIT;

Answer 1

The query is ordering by the difference between a string and a float. This odd calculation confuses and angers MySQL and results in a slow filesort.
mysql> explain select ABS(propertyCoordinatesLat - 3.33234) as diff from property order by diff
+----+-------------+----------+------------+-------+---------------+--------------------------+---------+------+------+----------+-----------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+----------+------------+-------+---------------+--------------------------+---------+------+------+----------+-----------------------------+
| 1 | SIMPLE | property | NULL | index | NULL | propertyCoordinatesLat_2 | 302 | NULL | 1 | 100.00 | Using index; Using filesort |
+----+-------------+----------+------------+-------+---------------+--------------------------+---------+------+------+----------+-----------------------------+
Changing propertyCoordinatesLat and propertyCoordinatesLng to a more sensible numeric type lets MySQL optimize better. No more filesort. This should perform much better.
alter table property change propertyCoordinatesLat propertyCoordinatesLat numeric(10,8) not null;
alter table property change propertyCoordinatesLng propertyCoordinatesLng numeric(11,8) not null;
mysql> explain select ABS(propertyCoordinatesLat - 3.33234) as diff from property order by propertyCoordinatesLat asc limit 0,20;
+----+-------------+----------+------------+-------+---------------+--------------------------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+----------+------------+-------+---------------+--------------------------+---------+------+------+----------+-------------+
| 1 | SIMPLE | property | NULL | index | NULL | propertyCoordinatesLat_2 | 5 | NULL | 1 | 100.00 | Using index |
+----+-------------+----------+------------+-------+---------------+--------------------------+---------+------+------+----------+-------------+
If you want to get fancy, look into MySQL's spatial types. These will probably perform better, and definitely be more accurate.