MySQL中如何达成多表查询操作

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create table department(
id int,
name varchar(20)
);
create table employee(
id int primary key auto_increment,
name varchar(20),
sex enum('male','female') not null default 'male',
age int,
dep_id int
);
#插入数据
insert into department values
(200,'技术'),
(201,'人力资源'),
(202,'销售'),
(203,'运营');
insert into employee(name,sex,age,dep_id) values
('egon','male',18,200),
('alex','female',48,201),
('wupeiqi','male',38,201),
('yuanhao','female',28,202),
('nvshen','male',18,200),
('xiaomage','female',18,204)
;
# 查看表结构和数据
mysql> desc department;
+-------+-------------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id  | int(11)   | YES |   | NULL  |    |
| name | varchar(20) | YES |   | NULL  |    |
+-------+-------------+------+-----+---------+-------+
2 rows in set (0.19 sec)
mysql> desc employee;
+--------+-----------------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra     |
+--------+-----------------------+------+-----+---------+----------------+
| id   | int(11)        | NO  | PRI | NULL  | auto_increment |
| name  | varchar(20)      | YES |   | NULL  |        |
| sex  | enum('male','female') | NO  |   | male  |        |
| age  | int(11)        | YES |   | NULL  |        |
| dep_id | int(11)        | YES |   | NULL  |        |
+--------+-----------------------+------+-----+---------+----------------+
5 rows in set (0.01 sec)
mysql> select * from department;
+------+--------------+
| id  | name     |
+------+--------------+
| 200 | 技术     |
| 201 | 人力资源   |
| 202 | 销售     |
| 203 | 运营     |
+------+--------------+
4 rows in set (0.02 sec)
mysql> select * from employee;
+----+----------+--------+------+--------+
| id | name   | sex  | age | dep_id |
+----+----------+--------+------+--------+
| 1 | egon   | male  |  18 |  200 |
| 2 | alex   | female |  48 |  201 |
| 3 | wupeiqi | male  |  38 |  201 |
| 4 | yuanhao | female |  28 |  202 |
| 5 | nvshen  | male  |  18 |  200 |
| 6 | xiaomage | female |  18 |  204 |
+----+----------+--------+------+--------+
6 rows in set (0.00 sec)
ps:观察两张表，发现department表中id=203部门在employee中没有对应的员工，发现employee中id=6的员工在department表中没有对应关系。