mysql续集4-多表连接

1.多表连接查询

1.1准备表

#建表
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),
(‘liwenzhou‘,‘male‘,18,200),
(‘jingliyang‘,‘female‘,18,204)
;

mysql> select * from department;
+------+--------------+
| id | name |
+------+--------------+
| 200 | 技术 |
| 201 | 人力资源 |
| 202 | 销售 |
| 203 | 运营 |
+------+--------------+

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 |
+----+------------+--------+------+--------+

1.2多表连接

1.2.1语法

SELECT 字段列表
    FROM 表1 INNER|LEFT|RIGHT JOIN 表2
    ON 表1.字段 = 表2.字段;

1.2.2笛卡尔积

mysql> select * from employee,department;
+----+------------+--------+------+--------+------+--------------+
| id | name       | sex    | age  | dep_id | id   | name         |
+----+------------+--------+------+--------+------+--------------+
|  1 | egon       | male   |   18 |    200 |  200 | 技术         |
|  1 | egon       | male   |   18 |    200 |  201 | 人力资源     |
|  1 | egon       | male   |   18 |    200 |  202 | 销售         |
|  1 | egon       | male   |   18 |    200 |  203 | 运营         |
|  2 | alex       | female |   48 |    201 |  200 | 技术         |
|  2 | alex       | female |   48 |    201 |  201 | 人力资源     |
|  2 | alex       | female |   48 |    201 |  202 | 销售         |
|  2 | alex       | female |   48 |    201 |  203 | 运营         |
|  3 | wupeiqi    | male   |   38 |    201 |  200 | 技术         |
|  3 | wupeiqi    | male   |   38 |    201 |  201 | 人力资源     |
|  3 | wupeiqi    | male   |   38 |    201 |  202 | 销售         |
|  3 | wupeiqi    | male   |   38 |    201 |  203 | 运营         |
|  4 | yuanhao    | female |   28 |    202 |  200 | 技术         |
|  4 | yuanhao    | female |   28 |    202 |  201 | 人力资源     |
|  4 | yuanhao    | female |   28 |    202 |  202 | 销售         |
|  4 | yuanhao    | female |   28 |    202 |  203 | 运营         |
|  5 | liwenzhou  | male   |   18 |    200 |  200 | 技术         |
|  5 | liwenzhou  | male   |   18 |    200 |  201 | 人力资源     |
|  5 | liwenzhou  | male   |   18 |    200 |  202 | 销售         |
|  5 | liwenzhou  | male   |   18 |    200 |  203 | 运营         |
|  6 | jingliyang | female |   18 |    204 |  200 | 技术         |
|  6 | jingliyang | female |   18 |    204 |  201 | 人力资源     |
|  6 | jingliyang | female |   18 |    204 |  202 | 销售         |
|  6 | jingliyang | female |   18 |    204 |  203 | 运营         |
+----+------------+--------+------+--------+------+--------------+
24 rows in set (0.00 sec)

mysql>

1.2.3inner join

"取出两张表中共有的部分
employee表中有dep_id=204
department表中有id=203
这两条是非共有数据"
mysql> select * from employee e inner join department d on e.dep_id=d.id;
+----+-----------+--------+------+--------+------+--------------+
| id | name      | sex    | age  | dep_id | id   | name         |
+----+-----------+--------+------+--------+------+--------------+
|  1 | egon      | male   |   18 |    200 |  200 | 技术         |
|  2 | alex      | female |   48 |    201 |  201 | 人力资源     |
|  3 | wupeiqi   | male   |   38 |    201 |  201 | 人力资源     |
|  4 | yuanhao   | female |   28 |    202 |  202 | 销售         |
|  5 | liwenzhou | male   |   18 |    200 |  200 | 技术         |
+----+-----------+--------+------+--------+------+--------------+
5 rows in set (0.00 sec)

mysql>
或
mysql> select * from employee e,department d where e.dep_id=d.id;

1.2.4left join

"以左表为准，左表的数据会全部显示
employee表中dep_id为204的那条，也会存在了"
mysql> select * from employee e left join department d on e.dep_id=d.id;
+----+------------+--------+------+--------+------+--------------+
| id | name       | sex    | age  | dep_id | id   | name         |
+----+------------+--------+------+--------+------+--------------+
|  1 | egon       | male   |   18 |    200 |  200 | 技术         |
|  5 | liwenzhou  | male   |   18 |    200 |  200 | 技术         |
|  2 | alex       | female |   48 |    201 |  201 | 人力资源     |
|  3 | wupeiqi    | male   |   38 |    201 |  201 | 人力资源     |
|  4 | yuanhao    | female |   28 |    202 |  202 | 销售         |
|  6 | jingliyang | female |   18 |    204 | NULL | NULL         |
+----+------------+--------+------+--------+------+--------------+
6 rows in set (0.00 sec)

mysql>

1.2.5right join

"以右表为准，右表中的数据全部显示
department表中id=203那条也会存在"
mysql> select * from employee e right join department d on e.dep_id=d.id;
+------+-----------+--------+------+--------+------+--------------+
| id   | name      | sex    | age  | dep_id | id   | name         |
+------+-----------+--------+------+--------+------+--------------+
|    1 | egon      | male   |   18 |    200 |  200 | 技术         |
|    2 | alex      | female |   48 |    201 |  201 | 人力资源     |
|    3 | wupeiqi   | male   |   38 |    201 |  201 | 人力资源     |
|    4 | yuanhao   | female |   28 |    202 |  202 | 销售         |
|    5 | liwenzhou | male   |   18 |    200 |  200 | 技术         |
| NULL | NULL      | NULL   | NULL |   NULL |  203 | 运营         |
+------+-----------+--------+------+--------+------+--------------+
6 rows in set (0.00 sec)

mysql>

1.2.6全外连接

"显示左右两个表中的全部记录
mysql中不支持全外连接 full join
mysql可以使用下面的方式实现全外连接"

mysql> select * from employee e right join department d on e.dep_id=d.id
    -> union
    -> select * from employee e left join department d on e.dep_id=d.id;
+------+------------+--------+------+--------+------+--------------+
| id   | name       | sex    | age  | dep_id | id   | name         |
+------+------------+--------+------+--------+------+--------------+
|    1 | egon       | male   |   18 |    200 |  200 | 技术         |
|    2 | alex       | female |   48 |    201 |  201 | 人力资源     |
|    3 | wupeiqi    | male   |   38 |    201 |  201 | 人力资源     |
|    4 | yuanhao    | female |   28 |    202 |  202 | 销售         |
|    5 | liwenzhou  | male   |   18 |    200 |  200 | 技术         |
| NULL | NULL       | NULL   | NULL |   NULL |  203 | 运营         |
|    6 | jingliyang | female |   18 |    204 | NULL | NULL         |
+------+------------+--------+------+--------+------+--------------+
7 rows in set (0.00 sec)

mysql> 

"union与union all的区别：union会去掉相同的记录"
mysql> select * from employee e right join department d on e.dep_id=d.id union all select * from employee e left joinn department d on e.dep_id=d.id;
+------+------------+--------+------+--------+------+--------------+
| id   | name       | sex    | age  | dep_id | id   | name         |
+------+------------+--------+------+--------+------+--------------+
|    1 | egon       | male   |   18 |    200 |  200 | 技术         |
|    2 | alex       | female |   48 |    201 |  201 | 人力资源     |
|    3 | wupeiqi    | male   |   38 |    201 |  201 | 人力资源     |
|    4 | yuanhao    | female |   28 |    202 |  202 | 销售         |
|    5 | liwenzhou  | male   |   18 |    200 |  200 | 技术         |
| NULL | NULL       | NULL   | NULL |   NULL |  203 | 运营         |
|    1 | egon       | male   |   18 |    200 |  200 | 技术         |
|    5 | liwenzhou  | male   |   18 |    200 |  200 | 技术         |
|    2 | alex       | female |   48 |    201 |  201 | 人力资源     |
|    3 | wupeiqi    | male   |   38 |    201 |  201 | 人力资源     |
|    4 | yuanhao    | female |   28 |    202 |  202 | 销售         |
|    6 | jingliyang | female |   18 |    204 | NULL | NULL         |
+------+------------+--------+------+--------+------+--------------+
12 rows in set (0.00 sec)

mysql>

1.2.7符合条件的连接查询

"#示例1：以内连接的方式查询employee和department表，并且employee表中的age字段值必须大于25,即找出年龄大于25岁的员工以及员工所在的部门"
mysql> select * from employee e right join department d on e.dep_id=d.id where age>25;
+------+---------+--------+------+--------+------+--------------+
| id   | name    | sex    | age  | dep_id | id   | name         |
+------+---------+--------+------+--------+------+--------------+
|    2 | alex    | female |   48 |    201 |  201 | 人力资源     |
|    3 | wupeiqi | male   |   38 |    201 |  201 | 人力资源     |
|    4 | yuanhao | female |   28 |    202 |  202 | 销售         |
+------+---------+--------+------+--------+------+--------------+
3 rows in set (0.00 sec)

mysql> 

"示例2：以内连接的方式查询employee和department表，并且以age字段的升序方式显示"
mysql> select * from employee e right join department d on e.dep_id=d.id where age>25 order by age desc;
+------+---------+--------+------+--------+------+--------------+
| id   | name    | sex    | age  | dep_id | id   | name         |
+------+---------+--------+------+--------+------+--------------+
|    2 | alex    | female |   48 |    201 |  201 | 人力资源     |
|    3 | wupeiqi | male   |   38 |    201 |  201 | 人力资源     |
|    4 | yuanhao | female |   28 |    202 |  202 | 销售         |
+------+---------+--------+------+--------+------+--------------+
3 rows in set (0.00 sec)

mysql>

原文地址：https://blog.51cto.com/10983441/2399316

时间： 2024-11-05 19:25:55

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