INNER JOIN（内连接）

--用户表 user_info
create table user_info
(

user_id int,
user_name nvarchar(10)

);

insert into user_info
values
(1,N'张三'),
(2,N'李四'),
(3,N'王五');

--订单表
create table order_info
(

order_id int,
user_id int, --关联用户表
order_name nvarchar(20)

);

insert into order_info
values
(101,1,N'手机'),
(102,2,N'耳机'),
(103,2,N'电脑');

select
u.user_id,
u.user_name,
o.order_name
from user_info u
inner join order_info o
on u.user_id = o.user_id;

select
user_info.user_id,
user_info.user_name,
order_info.order_name
from user_info
inner join order_info
on user_info.user_id = order_info.user_id;