mysql多表联合查询

创建表a插入数据

create table a(
    `id` int(11) primary key ,
    `name` varchar(6) not null ,
    `age` int(4) not null
);
insert into a values (1,'111',20);
insert into a values (2,'222',20);
insert into a values (3,'333',20);
insert into a values (4,'444',20);

创建表b插入数据

create table  b(
    `id` int(11) primary key ,
    `result` float
);
insert into b values (1,11);
insert into b values (2,22);
insert into b values (5,11);

.内连接：INNER JOIN 求两个表的交集

select a.id,name,age,result
from a inner join b
on a.id = b.id;

	id	name	age	result
1	1	111	20	11
2	2	222	20	22

LEFT JOIN 求两个表的交集外加左表剩下的数据

select a.id,name,age,result
from a left join b
on a.id = b.id;

	id	name	age	result
1	1	111	20	11
2	2	222	20	22
3	3	333	null	null
4	4	444	null	null

RIGHT JOIN 两个表的交集外加右表剩下的数据

select a.id,name,age,result
from a right join b
on a.id = b.id;

	id	name	age	result
1	1	111	20	11
2	2	222	20	22
3	null	null	null	11

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