连接查询

mysql4.1可嵌套多个查询

一、内连接查询

(1)delect bookid ,borrowTime,backTime,ifbak,bookname,author,price 

from tb_borrow,tb_bookinfo where tb_borrow.bookid=tb_bookinfo.id；

二、子查询

(1)带in或not in

select id,bookname,author

from tb_bookinfo where id in(select bookid from tb_borrow);

(2)带比较运算符的子查询

（1）select score from tb_grade where name='优秀';

（2）select * from  tb_student

　　  where score >= (select score from tb_grade where name='优秀')

(3)带exists   (not exists)

使用exist是关键字，内层查询语句不返回查询记录，而是返回一个真假值。返回真时：外层查询语句继续查询，返回false：外层查询不做任何查询或查不出任何记录；

select id,bookname,author,price from tb_bookinfo

where exists (select * from tb_borrow where tb_borrow.bookid=tb_bookinfo.id);

(4)any  或all

列名  比较运算符   any（子查询）

select * from tb_student1

where score > any(select score from tb_student1 where classid=13）；