1练习如何判断是函数还是方法？
from types import FunctionType,MethodType
class A:
def func(self):
pass
a = A()
print(isinstance(a.func,FunctionType))
print(isinstance(a.func,MethodType))
print(isinstance(A.func,FunctionType))
print(isinstance(A.func,MethodType))
2主键和外键的区别：
主键：一张表只能有一个主键，主键非空且唯一；
外键：一张表可以有多个外键，也可以重复
数据库语言的三大类：
DDL：
数据库定义语言：数据库，表的创建
create
alter
drop
show/desc
DML:Data Manipulation Language,
数据库操作语言：数据记录的操作
insert
update
delete
selete
DCL:
数据库控制语言 用户的创建以及授权
内容概览：
记录的操作：
插入数据：
insert into
更新数据：
update set
删除数据
delete from xx.xx where xxx
查询数据：
单表查询
多表查询
单表查询：
select distinct
from
where
group by
having
order by
limit
多表查询：
select 字段
from 表1 inner/letf/right join 表2
on 表1.字段 = 表2.字段
交叉连接：
select * from employee,department;
内连接
inner join
左连接
left join
右连接
right join
全外连接
left join
union
right join
子查询：
IN关键字的子查询
带比较运算符的子查询
EXISTS关键字的子查询
create table employee(
id int not null unique auto_increment,
emp_name varchar(20) not null,
sex enum('male','female') not null default 'male',
age int(3) unsigned not null,
post varchar(50),
post_comment varchar(100),
salary double(15,2),
office int,
depart_id int
);
alter table employee add hire_date date not null after age;
insert into employee(emp_name,sex,age,hire_date,post,salary,office,depart_id) values
('egon','male',18,'20170301','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);
select (
case
when emp_name = 'jiingliyang'
then emp_name
when emp_name = 'alex'
then concat(emp_name,'_bigSB')
else
concat(emp_name,'sb')
end) as new_name
from employee;
select concat ('<名字:',emp_name,'> <薪资:',salary) from employee;
select distinct post from employee;
select emp_name,salary*12 as annual_year from employee;
select emp_name from employee where post = 'sale';
select emp_name,salary from employee where post = 'teacher' and salary >10000;
select emp_name,salary from employee where salary between 10000 and 20000;
select emp_name,post_comment from employee where post_comment is null;
update employee set post_comment='good' where id < 5;
select emp_name,salary from employee where salary = 3000 or salary = 3500 or salary = 4000;
select emp_name,salary from employee where salary in (300,3500,4000,9000);
select emp_name,salary from employee where salary not in (300,3500,4000,9000);
select * from employee where emp_name like 'eg%';
select * from employee where emp_name like 'al__';
select emp_name,age from employee where post = 'teacher';
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
);
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','female',18,200),
('alex','male',48,201),
('wupeiqi','male',38,201),
('yuanhao','female',28,202),
('liwewzhou','male',18,200),
('jinliyang','female',18,204);
select employee.id,employee.name,employee.age,employee.sex,department.name from employee,department where employee.dep_id = department.id;
select * from employee left join department on employee.dep_id = department.id
union
select * from employee right join department on employee.dep_id = department.id;
select employee.name,department.name from employee inner join department
on employee.dep_id = department.id
where age > 25;
select employee.name,employee.age,employee.sex department.name from employee inner join department
on employee.dep_id = department.id
where age > 25;
select employee.name as staff_name,department.name as department_name from employee inner join department
on employee.dep_id = department.id
where age > 25;
select employee.id,employee.name,employee.age,department.name from employee,department
where employee.dep_id = department.id
and age >25
order by age asc;
select id,name from department where id in
(select dep_id from employee group by dep_id having avg(age) >25);
select id,name from employee where dep_id in
(select id from department where name = '技术');
select name from department where id not in
(select distinct dep_id from employee);
select name,age from employee where age >
(select avg(age) from employee);
select t1.name,t1.age from employee t1
inner join
(select dep_id,avg(age) avg_age from employee group by dep_id) t2
on t1.dep_id = t2.dep_id
where t1.age > t2.avg_age;
select employee.name,employee.age from employee;
alter table employee rename employee__1;
SELECT
*
FROM
employee AS t1
INNER JOIN (
SELECT
post,
max(hire_date) max_date
FROM
employee
GROUP BY
post
) AS t2 ON t1.post = t2.post
WHERE
t1.hire_date = t2.max_date;
select * from employee as t1
inner join
(select post,max(hire_date) max_date from employee group by post) as t2
on t1.post = t2.post
where t1.hire_date = t2.max_date;
source C:/Program Files/mysql-5.6.41-winx64/data/init.sql
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
);
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)
;
insert into department values
(200,'技术'),
(201,'人力资源'),
(202,'销售'),
(203,'运营');
交叉连接 生成笛卡尔积
select * from employee,department;
select employee.id,employee.name,employee.age,employee.sex,department.name depart_name from employee
inner join department on employee.dep_id = department.id;
select employee.id,employee.name,employee.age,employee.sex,department.name depart_name from employee
left join department on employee.dep_id = department.id;
select employee.id,employee.name,employee.age,employee.sex,department.name depart_name from employee
right join department on employee.dep_id = department.id;
select * from employee left join department on employee.dep_id = department.id
union
select * from employee right join department on employee.dep_id = department.id
select employee.name,department.name as department_name from employee left join department
on employee.dep_id = department.id where age > 25;
select * from employee left join department
on employee.dep_id = department.id where age > 25 order by age desc;
select dep_id from employee group by dep_id having avg(age) > 25;
select name from employee where dep_id in (
select id from department where name = '技术');
select name from department where id not in (select distinct dep_id from employee);
select name,age from employee where age > (select avg(age) from employee);
select t1.name,t1.age from employee t1
inner join
(select dep_id,avg(age) avg_age from employee group by dep_id) t2
on t1.dep_id = t2.dep_id
where t1.age > t2.avg_age;
select * from employee
where exists
(select id from department where id = 200);
create table employee2(
id int not null unique auto_increment,
name varchar(20) not null,
sex enum('male','female') not null default 'male',
age int(3) unsigned not null default 28,
hire_date date not null,
post varchar(50),
post_commenrt varchar(100),
salary double(15,2),
office int,
depart_id int);
insert into employee2(name,sex,age,hire_date,post,salary,office,depart_id) values
('egon','male',18,'20170301','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)
;
找出每个部门中入职时间最久的员工
先按照部门分组 找出该部门中时间最久的职位select post,max(hire_date) max_hiredate from employee2 group by post
与原来的员工数据表连接 连接的关键字是post
然后再筛选
筛选的条件是入职时间相等
select * from employee2 as t1
inner join (select post,max(hire_date) max_hiredate from employee2 group by post) as t2 on t1.post = t2.post
where t1.hire_date = t2.max_hiredate;
SELECT
*
FROM
employee2 AS t1
INNER JOIN (
SELECT
post,
max(hire_date) max_date
FROM
employee2
GROUP BY
post
) AS t2 ON t1.post = t2.post
WHERE
t1.hire_date = t2.max_date;