mysql 去重复查询 子查询

SELECT
e.id,
e.on_line,
e.name,
(SELECT d.longitude FROM sys_equipment_data d WHERE d.equipment_id = e.id ORDER BY d.transmission_time DESC LIMIT 1) AS longitude,
(SELECT d.latitude FROM sys_equipment_data d WHERE d.equipment_id = e.id ORDER BY d.transmission_time DESC LIMIT 1) AS latitude
FROM
sys_equipment e

 事实证明同样的查询结果关联查询要比子查询耗时。