mysql left join查询

表1：wd_device设备表

表2：wd_heartrae心率表

HR_DID代表设备表的ID编号

D_DeviceCode：设备表的设备编号

SELECT a.id,a.D_DeviceCode,b.* FROM wd_device a

LEFT JOIN (SELECT * FROM wd_heartrate) b ON b.HR_DID=a.ID