mysql 取两点之间的距离，单位为: 米

st_distance_sphere(point(a.jd, a.wd), point(b.jd, b.dw))

示例：

set @p1=point(118.659802, 24.885497);
set @p2=point(118.671475, 24.867432);
select st_distance_sphere(@p1,@p2) 

结果：
2328.436587875269