Question

I have a phpmyadmin database with 1 000 000 record i need to search in. Every week there are 500 000 records added.

so, this is what I need:

location_id value   date        time        name                lat     lng
3            234    2011-11-18  19:50:00    Amerongen beneden   5.40453 51.97486
4            594    2011-11-18  19:50:00    Amerongen boven     5.41194 51.97507

I do this with this query:

SELECT location_id, value, date, time, locations.name, locations.lat, locations.lng FROM
(
SELECT location_id, value, date, time from `measurements` 
LEFT JOIN units ON (units.id = measurements.unit_id)
WHERE units.name='Waterhoogte'
ORDER BY measurements.date DESC, measurements.time DESC
) as last_record
LEFT JOIN locations on (locations.id = location_id)
GROUP BY location_id

which takes 30 seconds. How can I improve this? This is my structure:

CREATE TABLE IF NOT EXISTS `locations` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) NOT NULL,
  `code` varchar(255) NOT NULL,
  `lat` varchar(10) NOT NULL,
  `lng` varchar(10) NOT NULL,
  `owner_id` int(11) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=244 ;

-- --------------------------------------------------------

--
-- Table structure for table `measurements`  
--

CREATE TABLE IF NOT EXISTS `measurements` (
  `id` int(11) NOT NULL auto_increment,
  `date` date NOT NULL,
  `time` time NOT NULL,
  `value` varchar(255) NOT NULL,
  `location_id` int(11) NOT NULL,
  `unit_id` int(11) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=676801 ;

-- --------------------------------------------------------

--
-- Table structure for table `owner`
--

CREATE TABLE IF NOT EXISTS `owner` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ;

-- --------------------------------------------------------

--
-- Table structure for table `units`
--

CREATE TABLE IF NOT EXISTS `units` (
  `id` int(11) NOT NULL auto_increment,
  `name` varchar(255) NOT NULL,
  `description` text NOT NULL,
  `unit_short` varchar(255) NOT NULL,
  `owner_id` int(11) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=latin1 AUTO_INCREMENT=44 ;

What is the limit what phpmyadmin can handle?

Answer 1

Create an index on units.name specifically is a good start.
You should also really rethink the amount of data you are pulling back.
Is someone really going to sift through that many records. Change your query to limit the number of records and think of a UI interface that involves a paging mechanism.