【MySQL复习】嵌套查询&内连接查询&外连接查询
一、嵌套连接
select * from user where cid = (select id from class where cName='1班';
查询1班的学生信息
二、内连接
select * from user inner join class where user.cid = class.id and class.cName = '1班';
同理:
select * from user,class where user.cid = class.id and class.cName = '1班';
也可以起别名
select s.name,s.id,c.cName from user as s,class as c where s.cid = c.id and c.cName = '1班';
三、外连接
左连接:左表的所有数据和右表满足条件的数据
select * from student as s left join class as c where s.cid = c.id and s.id = 1;
右链接:右表的所有数据和左表满足条件的数据
注:一般使用内连接进行查询,外连接在特殊情况使用!
本文来自博客园,作者:小李不背锅,转载请注明原文链接:https://www.cnblogs.com/lishilin-glut/p/15945202.html