mysql 数据库 IV（多表查询）

1.今日内容

1. 多表联合查询

   • 内连接 (inner jion ...on ...) ：只连接匹配的行
   • 外连接：只连接匹配的行
     • 左外连接 left jion ... on ...
     • 右外连接 right jion ... on ...
     • 全外连接 full jion

   select 字段列表 from 表1 inner|left|right join 
                                       表2 on 表1.字段 = 表2.字段

2. 子查询

2.具体内容

1. 数据准备

   
   

   数据准备示例

   mysql> use day41;
   Database changed
   
   
   # 建表
   mysql> create table department(
       -> id int,
       -> name varchar(20) 
       -> );
   Query OK, 0 rows affected (0.05 sec)
   
   mysql> 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
       -> );
   Query OK, 0 rows affected (0.02 sec)
   
   # 插入数据
   mysql> insert into department values
       -> (200,'技术'),
       -> (201,'人力资源'),
       -> (202,'销售'),
       -> (203,'运营');
   Query OK, 4 rows affected (0.01 sec)
   Records: 4  Duplicates: 0  Warnings: 0
   
   mysql> 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),
       -> ('liwenzhou','male',18,200),
       -> ('jingliyang','female',18,204)
       -> ;
   Query OK, 6 rows affected (0.00 sec)
   Records: 6  Duplicates: 0  Warnings: 0
   
   # 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 (0.01 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 (0.00 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 (0.00 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 | liwenzhou  | male   |   18 |    200 |
   |  6 | jingliyang | female |   18 |    204 |
   +----+------------+--------+------+--------+
   6 rows in set (0.00 sec)

来源：https://www.cnblogs.com/xiaohei-chen/p/12193550.html