mysql 中sql语句关键字的书写顺序与执行顺序
书写顺序：
select -> from -> where -> group by -> having -> order by
执行顺序：
from -> where -> group by -> having -> select -> order by
书写顺序：
select -> from -> where -> group by -> having -> order by
执行顺序：
from -> where -> group by -> having -> select -> order by
