先说ex**ts 英文存在的意思, 父查询where not ex**ts(子查询)---不存在子查询则满足父查询出发条件,where 字段 not in(子查询),如 select * from表名 where 学号 not in(select学号from表名where成绩60的人的信息,,----------不知道我举得例子你看明白没
growing up in the usa,i was ashamed of my mother’s chinese engl**h.because of her she was often treated ...my mother has realized the limitations of her ...