CREATE TABLE air
(id INT AUTO_INCREMENT, latlng varchar(50), pm int, datestamp datetime, PRIMARY KEY (id) )
;
INSERT INTO air
(latlng, pm, datestamp)
values
('20,30',	10	,	'2016-05-22 00:00:00')	,
('20,30',	50	,	'2016-05-22 10:10:00')	,
('20,30',	40	,	'2016-05-22 10:30:00')	;
-- 原查詢語法: 舊紀錄在前
-- SELECT * FROM `air`;
 
-- 查詢語法2: 新紀錄在前
SELECT tmp.* FROM 
( SELECT * FROM `air` ORDER BY `datestamp`
) tmp GROUP BY `latlng` ;

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