# 创建一个user表
create table users(
id int primary key auto_increment,
name varchar(20),
dpt_id int
);
# 向user表中插入数据
insert into users values
(null,'刘备',1),
(null,'关羽',2),
(null,'赵飞',2),
(null,'吕布',2),
(null,'小乔',3),
(null,'大乔',3);
# 创建一个department表
create table department(
id int primary key auto_increment,
name varchar(20)
);
# 向department表中插入数据
insert into department values
(null,'指挥部'),
(null,'作战部'),
(null,'后勤部');
# 查询 users 表中的第三和第四条数据 (第一个数字是偏移量,第二个数字是查询几条)
select * from users limit 2,2;
# 为users表取别名
select u.name from users as u;
# 为users表中的字段取别名
select name as '姓名', dpt_id as '部门' from users;
# 表的关联查询 查询users表中员工的姓名和所在的部门
select u.name as '姓名',d.name as '部门' from users as u inner join department as d where u.dpt_id = d.id;
# 表的关联查询 查询users表中吕布所在的部门 (on 可以换成 where)
select d.name from department as d inner join users as u on u.dpt_id=d.id and u.name='吕布';