多表一对一左关联

SQL:　　　　　　select * from equi left join client_user on equi.equi_userid=client_user.id left join equi_sensor on equi.sensor=equi_sensor.id left join equi_model on equi.equi_type=equi_model.id;

Controller:　

/**
 *关联查询
 * 查询设备信息
 * 查询设备所属的用户
 * 查询设备的类型
 * 查询设备的传感器信息
 */
@RequestMapping("/findEquiClient")
@ResponseBody
public String findEquiClient()throws Exception{
  List<Map<String,Object> > list = equiService.findEquiClient();
    return JSON.toJSONString(list);
}

Mapper:

@Override
public List<Map<String, Object>> findEquiClient() {
    return equiMapper.findEquiClient();
}
mapper.xml:

<select id="findEquiClient" resultType="HashMap">
 select * from
 equi
 left join client_user on equi.equi_userid=client_user.id
 left join equi_sensor on equi.sensor=equi_sensor.id
 left join equi_model on equi.equi_type=equi_model.id
</select>
也可使用：