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MAX(<date>) / GROUP BY behaviour...

I'm attempting to retrieve the latest records for each pairs for key1 and key2 using the following select query:

SELECT `key1`, `key2`, MAX(`key3`) AS `date`, `date1`, `date2`, `date3`, `date4` 
FROM `test`
GROUP BY `key1`, `key2`;

The results I get as shown below are somewhat confusing. I do get the latest date but the values for the columns date1, date2, date3 and date4 are not matching the records I would expect from the database.

key1key2datedate1date2date3date4
100B2099-01-012000-07-112000-12-312000-07-112000-12-31
400B2099-05-042000-07-182000-07-182000-07-182000-07-18

I'm no SQL expert so Any help would be quite appreciated !

Robert.

Bellow is a sample DB 

Server version: 5.5.52-MariaDB - MariaDB Server

CREATE TABLE IF NOT EXISTS `test` (
  `key1` int(10) unsigned NOT NULL,
  `key2` varchar(5) NOT NULL,
  `key3` date NOT NULL,
  `date1` date DEFAULT NULL,
  `date2` date DEFAULT NULL,
  `date3` date DEFAULT NULL,
  `date4` date DEFAULT NULL,
  PRIMARY KEY (`key1`,`key2`,`key3`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `test` (`key1`,`key2`,`key3`, `date1`, `date2`, `date3`, `date4`)
VALUES
	( 100, 'B', '2000-01-01', '2000-07-11', '2000-12-31', '2000-07-11', '2000-12-31' ),
	( 100, 'B', '2099-01-01', '2014-08-30', '2014-12-31', '2014-08-20', '2014-12-31' ),
	
	( 400, 'B', '2000-05-01', '2000-07-18', '2000-07-18', '2000-07-18', '2000-07-18' ),
	( 400, 'B', '2099-05-04', '2014-10-18', '2014-11-25', '2014-09-18', '2014-09-30' );

Answer Answered by Brian Evans in this comment.

While it is an error in standard SQL, which can be enabled by sql_mode=STRICT, MySQL and MariaDB allow non-aggregate columns that are not included in the GROUP BY clause.

The values that the non-aggregate columns include are completely random and not necessarily related to, as in your case, a single row with the aggregate function result.

If you rewrite the query, you'll get consistent results:

SELECT `key1`, `key2`, `key3` `date`, `date1`, `date2`, `date3`, `date4`
from test JOIN(SELECT `key1`, `key2`, MAX(`key3`) `key3` FROM `test`
GROUP BY `key1`, `key2`) `d1` USING (`key1`, `key2`, `key3`) ;

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