项目中遇到这样的要求,
从数据表里查出每台机器的最后一次链接时间
必须group by机器id order by connect_time
"SELECT `c`.*,`d`.`equipment_type` FROM `ms_gateway_connect` c
LEFT JOIN `ms_gateway_device` `d` ON `c`.`equipment_id`=`d`.`equipment_id`
WHERE `c`.`id` =
( SELECT id FROM `ms_gateway_connect` gc
WHERE `gc`.`equipment_id` = `c`.`equipment_id`
ORDER BY `gc`.`connect_time` DESC limit 1)
and `c`.`equipment_id` <> '' GROUP BY `c`.`equipment_id`"