一、准备表
#建表
create table dept(
id int primary key not null auto_increment,
name varchar(20) not null
);
create table employee(
id int primary key auto_increment,
name varchar(20) not null,
sex enum(‘male‘,‘female‘) not null default ‘male‘,
age int not null ,
dept_id int not null,
foreign key(dept_id) references dept(id)
on delete cascade
on update cascade
);
#插入数据
insert into dept(name) values
(‘技术‘),
(‘人力资源‘),
(‘销售‘),
(‘运营‘);
insert into employee(name,sex,age,dept_id) values
(‘egon‘,‘male‘,18,1),
(‘alex‘,‘female‘,48,2),
(‘wupeiqi‘,‘male‘,38,3),
(‘yuanhao‘,‘female‘,28,4),
(‘liwenzhou‘,‘male‘,18,1),
(‘jingliyang‘,‘female‘,18,3)
;
#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 | |
+-------+-------------+------+-----+---------+-------+
mysql> desc employee;
+---------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| sex | enum(‘male‘,‘female‘) | NO | | male | |
| age | int(11) | NO | | NULL | |
| dept_id | int(11) | NO | MUL | NULL | |
+---------+-----------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
mysql> select * from dept;
+----+----------+
| id | name |
+----+----------+
| 1 | 技术 |
| 2 | 人力资源 |
| 3 | 销售 |
| 4 | 运营 |
+----+----------+
4 rows in set (0.00 sec)
mysql> select * from employee;
+----+------------+--------+-----+---------+
| id | name | sex | age | dept_id |
+----+------------+--------+-----+---------+
| 1 | egon | male | 18 | 1 |
| 2 | alex | female | 48 | 2 |
| 3 | wupeiqi | male | 38 | 3 |
| 4 | yuanhao | female | 28 | 4 |
| 5 | liwenzhou | male | 18 | 1 |
| 6 | jingliyang | female | 18 | 3 |
+----+------------+--------+-----+---------+
6 rows in set (0.00 sec)
表department与employee二、多表连接查询
重点：外链接语法
SELECT 字段列表
FROM 表1 INNER|LEFT|RIGHT JOIN 表2
ON 表1.字段 = 表2.字段;- 交叉连接：不适用任何匹配条件。生成笛卡尔积,结果没有任何参考作用；
mysql> select * from dept, employee;
+----+----------+----+------------+--------+-----+---------+
| id | name | id | name | sex | age | dept_id |
+----+----------+----+------------+--------+-----+---------+
| 1 | 技术 | 1 | egon | male | 18 | 1 |
| 2 | 人力资源 | 1 | egon | male | 18 | 1 |
| 3 | 销售 | 1 | egon | male | 18 | 1 |
| 4 | 运营 | 1 | egon | male | 18 | 1 |
| 1 | 技术 | 2 | alex | female | 48 | 2 |
| 2 | 人力资源 | 2 | alex | female | 48 | 2 |
| 3 | 销售 | 2 | alex | female | 48 | 2 |
| 4 | 运营 | 2 | alex | female | 48 | 2 |
| 1 | 技术 | 3 | wupeiqi | male | 38 | 3 |
| 2 | 人力资源 | 3 | wupeiqi | male | 38 | 3 |
| 3 | 销售 | 3 | wupeiqi | male | 38 | 3 |
| 4 | 运营 | 3 | wupeiqi | male | 38 | 3 |
| 1 | 技术 | 4 | yuanhao | female | 28 | 4 |
| 2 | 人力资源 | 4 | yuanhao | female | 28 | 4 |
| 3 | 销售 | 4 | yuanhao | female | 28 | 4 |
| 4 | 运营 | 4 | yuanhao | female | 28 | 4 |
| 1 | 技术 | 5 | liwenzhou | male | 18 | 1 |
| 2 | 人力资源 | 5 | liwenzhou | male | 18 | 1 |
| 3 | 销售 | 5 | liwenzhou | male | 18 | 1 |
| 4 | 运营 | 5 | liwenzhou | male | 18 | 1 |
| 1 | 技术 | 6 | jingliyang | female | 18 | 3 |
| 2 | 人力资源 | 6 | jingliyang | female | 18 | 3 |
| 3 | 销售 | 6 | jingliyang | female | 18 | 3 |
| 4 | 运营 | 6 | jingliyang | female | 18 | 3 |
+----+----------+----+------------+--------+-----+---------+
24 rows in set (0.00 sec)- 内连接
# 按照where条件取出两张表共有的部分，相当于利用条件从笛卡尔积结果中筛选出了正确的结果
mysql> select * from dept, employee where dept.id = employee.dept_id;
# 效率较低，连表操作最好还是用inner jion；
#找两张表共有的部分，相当于利用条件从笛卡尔积结果中筛选出了正确的结果
#department没有204这个部门，因而employee表中关于204这条员工信息没有匹配出来
mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee inner join department on employee.dep_id=department.id;
+----+-----------+------+--------+--------------+
| id | name | age | sex | name |
+----+-----------+------+--------+--------------+
| 1 | egon | 18 | male | 技术 |
| 2 | alex | 48 | female | 人力资源 |
| 3 | wupeiqi | 38 | male | 人力资源 |
| 4 | yuanhao | 28 | female | 销售 |
| 5 | liwenzhou | 18 | male | 技术 |
+----+-----------+------+--------+--------------+
#上述sql等同于
mysql> select employee.id,employee.name,employee.age,employee.sex,department.name from employee,department where employee.dep_id=department.id;
+----+----------+----+------------+--------+-----+---------+
| id | name | id | name | sex | age | dept_id |
+----+----------+----+------------+--------+-----+---------+
| 1 | 技术 | 1 | egon | male | 18 | 1 |
| 1 | 技术 | 5 | liwenzhou | male | 18 | 1 |
| 2 | 人力资源 | 2 | alex | female | 48 | 2 |
| 3 | 销售 | 3 | wupeiqi | male | 38 | 3 |
| 3 | 销售 | 6 | jingliyang | female | 18 | 3 |
| 4 | 运营 | 4 | yuanhao | female | 28 | 4 |
+----+----------+----+------------+--------+-----+---------+- 外链接之左连接：优先显示左表全部记录
# 以左表为准，即找出所有员工信息，当然包括没有部门的员工
# 本质就是：在内连接的基础上增加左边有右边没有的结果
mysql> select employee.id, employee.name, employee.age, dept.name as dept
-> from employee right join dept
-> on employee.dept_id = dept.id;
+------+------------+------+----------+
| id | name | age | dept |
+------+------------+------+----------+
| 1 | egon | 18 | 技术 |
| 5 | liwenzhou | 18 | 技术 |
| 2 | alex | 48 | 人力资源 |
| 3 | wupeiqi | 38 | 销售 |
| 6 | jingliyang | 18 | 销售 |
| 4 | yuanhao | 28 | 运营 |
+------+------------+------+----------+
6 rows in set (0.00 sec)
- 外链接之右连接：优先显示右表全部记录
#以右表为准，即找出所有部门信息，包括没有员工的部门
#本质就是：在内连接的基础上增加右边有左边没有的结果
mysql> select employee.id,employee.name,dept.name as dept_name from employee right join dept on employee.dept_id=dept.id;
+------+------------+-----------+
| id | name | dept_name |
+------+------------+-----------+
| 1 | egon | 技术 |
| 5 | liwenzhou | 技术 |
| 2 | alex | 人力资源 |
| 3 | wupeiqi | 销售 |
| 6 | jingliyang | 销售 |
| 4 | yuanhao | 运营 |
| NULL | NULL | 支持 |
+------+------------+-----------+
7 rows in set (0.00 sec)- 全外连接：显示左右两个表全部记录
全外连接：在内连接的基础上增加左边有右边没有的和右边有左边没有的结果
#注意：mysql不支持全外连接 full JOIN
#强调：mysql可以使用此种方式间接实现全外连接
select * from employee left join dept on employee.dept_id = dept.id
union
select * from employee right join dept on employee.dep_id = dept.id
;
#查看结果
# 也包括没有员工的部门或不属于已知部门的员工;
mysql> select * from employee left join dept on employee.dept_id = dept.id union select * from employee right join dept on employee.dept_id = dept.id ;
+------+------------+--------+------+---------+------+----------+
| id | name | sex | age | dept_id | id | name |
+------+------------+--------+------+---------+------+----------+
| 1 | egon | male | 18 | 1 | 1 | 技术 |
| 5 | liwenzhou | male | 18 | 1 | 1 | 技术 |
| 2 | alex | female | 48 | 2 | 2 | 人力资源 |
| 3 | wupeiqi | male | 38 | 3 | 3 | 销售 |
| 6 | jingliyang | female | 18 | 3 | 3 | 销售 |
| 4 | yuanhao | female | 28 | 4 | 4 | 运营 |
| NULL | NULL | NULL | NULL | NULL | 5 | 支持 |
+------+------------+--------+------+---------+------+----------+
7 rows in set (0.00 sec)三、符合条件连接查询
#示例1：以内连接的方式查询employee和dept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 employee.id, employee.name as "员工", employee.age, dept.name as ‘部门‘ from employee right join dept
-> on employee.dept_id = dept.id
-> where age > 25 order by age;
+------+---------+------+----------+
| id | 员工 | age | 部门 |
+------+---------+------+----------+
| 2 | alex | 48 | 人力资源 |
| 3 | wupeiqi | 38 | 销售 |
| 4 | yuanhao | 28 | 运营 |
+------+---------+------+----------+
3 rows in set (0.00 sec)四、子查询
#1：子查询是将一个查询语句嵌套在另一个查询语句中。 #2：内层查询语句的查询结果，可以为外层查询语句提供查询条件。 #3：子查询中可以包含：IN、NOT IN、ANY、ALL、EXISTS 和 NOT EXISTS等关键字 #4：还可以包含比较运算符：= 、 !=、> 、<等
- 带IN关键字的子查询
# 查询平均年龄在25岁以上的部门名
select id,name from dept
where id in
(select dept_id from emp group by dept_id having avg(age) > 25);
# 查看技术部员工姓名
# 1. 找出技术部门的id；2.根据提供的部门id在员工表中查询符合条件的员工；
select name from emp
where dept_id in
(select id from dept where name=‘技术‘);
# 查看不足1人的部门名(子查询得到的是有人的部门id)
# 1.不足一人的部门id；2.根据id找到部门名称
mysql> select name from dept where id in (select dept_id as dept_num from emp group by dept_id having count(id) <=1);
+----------+
| name |
+----------+
| 人力资源 |
| 运营 |
+----------+
2 rows in set (0.00 sec)
- 带比较运算符的子查询
# 比较运算符：=、!=、>、>=、<、<=、<>
# 查询大于所有人平均年龄的员工的姓名与年龄
# 1、平均年龄； 2、在表中根据条件查询
mysql> select name, age from emp where age>(select avg(age) from emp);
+---------+-----+
| name | age |
+---------+-----+
| alex | 48 |
| wupeiqi | 38 |
+---------+-----+
2 rows in set (0.00 sec)
# 查询大于部门内平均年龄的员工姓名、年龄
- 带EXISTS关键字的子查询
EXISTS关字键字表示存在。在使用EXISTS关键字时，内层查询语句不返回查询的记录。 而是返回一个真假值。True或False 当返回True时，外层查询语句将进行查询；当返回值为False时，外层查询语句不进行查询
#department表中存在dept_id=203，Ture
mysql> select * from employee
-> where exists
-> (select id from department where id=200);
+----+------------+--------+------+--------+
| 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 |
+----+------------+--------+------+--------+
#department表中存在dept_id=205，False
mysql> select * from employee
-> where exists
-> (select id from department where id=204);
Empty set (0.00 sec)- 带EXIST
EXISTS关字键字表示存在。在使用EXISTS关键字时，内层查询语句不返回查询的记录。 而是返回一个真假值。True或False 当返回True时，外层查询语句将进行查询；当返回值为False时，外层查询语句不进行查询
mysql> select * from emp
-> where exists
-> (select id from dept where id = 1);
+----+------------+--------+-----+---------+
| id | name | sex | age | dept_id |
+----+------------+--------+-----+---------+
| 1 | egon | male | 18 | 1 |
| 2 | alex | female | 48 | 2 |
| 3 | wupeiqi | male | 38 | 3 |
| 4 | yuanhao | female | 28 | 4 |
| 5 | liwenzhou | male | 18 | 1 |
| 6 | jingliyang | female | 18 | 3 |
+----+------------+--------+-----+---------+
6 rows in set (0.00 sec)
mysql> select * from emp
-> where exists
-> (select id from dept where id = 10);
Empty set (0.00 sec)- 练习
查询每个部门最新入职的那位员工
# 1. 准备表格
company.employee
员工id id int
姓名 emp_name varchar
性别 sex enum
年龄 age int
入职日期 hire_date date
岗位 post varchar
职位描述 post_comment varchar
薪水 salary double
办公室 office int
部门编号 depart_id int
#创建表
create table employee(
id int not null unique auto_increment,
name varchar(20) not null,
sex enum(‘male‘,‘female‘) not null default ‘male‘, #大部分是男的
age int(3) unsigned not null default 28,
hire_date date not null,
post varchar(50),
post_comment varchar(100),
salary double(15,2),
office int, #一个部门一个屋子
depart_id int
);
#查看表结构
mysql> desc emp;
+--------------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(20) | NO | | NULL | |
| sex | enum(‘male‘,‘female‘) | NO | | male | |
| age | int(3) unsigned | NO | | 28 | |
| hire_date | date | NO | | NULL | |
| post | varchar(50) | YES | | NULL | |
| post_comment | varchar(100) | YES | | NULL | |
| salary | double(15,2) | YES | | NULL | |
| office | int(11) | YES | | NULL | |
| depart_id | int(11) | YES | | NULL | |
+--------------+-----------------------+------+-----+---------+----------------+
#插入记录
#三个部门：教学，销售，运营
insert into emp(name,sex,age,hire_date,post,salary,office,depart_id) values
(‘egon‘,‘male‘,18,‘20170301‘,‘老男孩驻沙河办事处外交大使‘,7300.33,401,1), #以下是教学部
(‘alex‘,‘male‘,78,‘20150302‘,‘teacher‘,1000000.31,401,1),
(‘wupeiqi‘,‘male‘,81,‘20130305‘,‘teacher‘,8300,401,1),
(‘yuanhao‘,‘male‘,73,‘20140701‘,‘teacher‘,3500,401,1),
(‘liwenzhou‘,‘male‘,28,‘20121101‘,‘teacher‘,2100,401,1),
(‘jingliyang‘,‘female‘,18,‘20110211‘,‘teacher‘,9000,401,1),
(‘jinxin‘,‘male‘,18,‘19000301‘,‘teacher‘,30000,401,1),
(‘成龙‘,‘male‘,48,‘20101111‘,‘teacher‘,10000,401,1),
(‘歪歪‘,‘female‘,48,‘20150311‘,‘sale‘,3000.13,402,2),#以下是销售部门
(‘丫丫‘,‘female‘,38,‘20101101‘,‘sale‘,2000.35,402,2),
(‘丁丁‘,‘female‘,18,‘20110312‘,‘sale‘,1000.37,402,2),
(‘星星‘,‘female‘,18,‘20160513‘,‘sale‘,3000.29,402,2),
(‘格格‘,‘female‘,28,‘20170127‘,‘sale‘,4000.33,402,2),
(‘张野‘,‘male‘,28,‘20160311‘,‘operation‘,10000.13,403,3), #以下是运营部门
(‘程咬金‘,‘male‘,18,‘19970312‘,‘operation‘,20000,403,3),
(‘程咬银‘,‘female‘,18,‘20130311‘,‘operation‘,19000,403,3),
(‘程咬铜‘,‘male‘,18,‘20150411‘,‘operation‘,18000,403,3),
(‘程咬铁‘,‘female‘,18,‘20140512‘,‘operation‘,17000,403,3)
;