MySQL中group by，on，where，join，order by，limit，having优先级
from > on > join > where > group by > having > select > distinct > order by > limit，详细https://blog.csdn.net/mine_song/article/details/70185744
from > on > join > where > group by > having > select > distinct > order by > limit，详细https://blog.csdn.net/mine_song/article/details/70185744
