select语法顺序
select [ALL | dostinct] {* | table.*} FROM table_name [as table_alias] [left | right | inner join table_name2] ---联合查询 [where ..] ---条件 [Group by ...] --指定结果按照哪几个字段分组 [Having] ---过滤分组的记录必须满足的次要条件 [Order by ...] ---指定查询记录按一个或多个条件排序 [Limit 1|2] ---记录从哪查到哪