一、建表
create table Guoji_A (
id bigint primary key AUTO_INCREMENT,
name varchar(20) ,
tel bigint
)
create table Guoji_B (
id bigint primary key AUTO_INCREMENT,
name varchar(20) ,
address bigint
)
二、插数据
insert into Guoji_A values (null,“大娃”,186),(null,“二娃”,187),(null,“三娃”,188),(null,“五娃”,189);
insert into Guoji_B values (null,“二娃”,10002),(null,“三娃”,10003),(null,“四娃”,10004);
三、表关联
select * from Guoji_A a left join Guoji_B b on a.name = b.name;
select * from Guoji_A a right join Guoji_B b on a.name = b.name;
☆☆☆☆☆☆mysql不支持全连接 用左连接联合右连接
select * from Guoji_A a LEFT JOIN Guoji_B b on a.name = b.name
UNION select * from Guoji_A a RIGHT JOIN Guoji_B b on a.name = b.name;
select * from Guoji_A a join Guoji_B b on a.name = b.name;
总结:
1、建表时 varchar 需要写字段最大长度;
2、插入数据时 主键id自增 ,只需写null
3、左连接,左表全有,右边缺的字段补null
右连接:右表全有,左边缺的字段补null
全连接(mysql不支持,可以通过union):左右表全有,缺字段补null
交集:join 左右表共有