day03 mysql navicat
A. The integrity constraints
Foreign key foreign key
A table (association table: the table is) set foreign key value field, corresponding to a record of another table (the table is associated with: a main table)
How to create two table?
First create the master table: because people want to associate you, you have to exist
> create table mas(id int primary key auto_increment, name varchar(20) not null, des varchar(30) not null);
Re-create the table:
> create table sla(
eid int primary key auto_increment,
name char(10) not null, age int not null,
mas_id int not null,
constraint fk_mas foreign key (mas_id) references mas (id) on delete cascade on update cascade # (constraint constraint) (reference Reference) (cascade cascade)
# Foreign key constraint name the foreign key (field) Which table (which field) synchronization delete synchronization update
);
How to insert data to two tables:
Give master data table inserted
> Insert into mas (name, des) values ( 'information unit', 'query planning information'), ( 'procurement', 'Buy query'), ( 'Technology', 'IT query');
Inserting data from the table to give
> insert into sla(name,age,mas_id) values('bajie',12,1),('wukong',13,3),('datang',14,2),('xixi',10,1),('haha',19,3),('lele',16,1);
How to delete records from two tables, delete timing
Record in the primary table
When the value of the primary table is a reference table from the field, when there is no reference from the table, can be deleted, otherwise an error
When you set up sync deleted from the table, synchronization update, delete and when it will do, casual, pay attention to the foreign key from the corresponding records in the table are all deleted: on delete cascade on update cascade // (cascade cascade )
Table associated with this: constraint fk_mas foreign key (mas_id) references mas (id) on delete cascade on update cascade // MUL
Add the phrase: it is the way to establish a complete association table
From the records of the table
When will delete all right, free
When more table time
Not suitable for the establishment of too many foreign keys
II. Variant foreign key three relationships
How to find out the relationship between the two tables
Suppose there are two tables: the left and right tables, analysis steps:
Step a: angle left standing on the table, if a plurality of records corresponding to a table on the left and right table, the table has a foreign key to the left
Step two: the right angle of the table stand, a plurality of records if the right table corresponds to a left table, the upper right table has a foreign key
Many-to-:
If steps one and two: there is only one true, then the relationship is a many (as many as can be understood as the state of the left and right interchangeable)
Book and Press relations:
一个出版社可以出版多本书
但是多个出版社不能出同一种书(除非是盗版)
如何建表:
先建立出版社
再建立书: 给书设置外键
多对多:
如果步骤一和步骤二: 同时成立,需要定义一个这两张表的关系表来专门存放二者的关系
作者和书的关系
一个作者可以写多本书
多个作者可以共同写一本书
如何建表:
创建两张关系表: 为两个普通表
额外建立第三张表: 设置两个外键分别对应两个关系表
代码:
建立三张表
> create table author(id int primary key auto_increment, name varchar(20));
> create table book(id int primary key auto_increment, name varchar(20));
> create table author_book(
id int primary key auto_increment,
book_id int not null,
author_id int not null,
constraint fk_book foreign key(book_id) references book(id) on delete cascade on update cascade,
constraint fk_author foreign key(author_id) references author(id) on delete cascade on update cascade
);
插入数据
> insert into author(name) values('八戒'),('悟空'),('大唐'),('溜溜');
> insert into book(name) values('一本书'),('两本书'),('三本书'),('四本书'),('五本书'),('六本书');
> insert into author_book(author_id,book_id) values(1,1),(1,2),(1,3),(1,4),(1,5),(1,6),(2,6),(3,4),(3,6),(4,1),(4,3);
一对一:
如果步骤一和步骤二: 都不成立,这种简单: 就是在左表foreign key基础上,再将外键字段设置唯一"unique"即可
用户和博客的关系
一个用户名只能注册同一个网站上的一个博客
如何建表:
先建立一张表
建立另一张表: 设置外键, 并且设置 unique
三.单表查询
1.单表查询的语法
select 字段1,字段2... from 表名
where 条件 //(condition 条件)
group by field
having 筛选
order by field
limit 显示限制条数
2.关键字的执行优先级
from //找到表
where //条件查询
group by //如果不分组, 则整体看做一组
having //将分组结果: 二次过滤
select //执行select,查询显示出来
distinct //去重: (distinct 不同的)
order by //按条件排序,然后可选升序或降序(默认升序)
limit //限制结果的显示条数
select group_concat(name),salary from employee where salary > 1000 group by salary having count(1) < 10 order by salary desc limit 3;
+--------------------+------------+
| group_concat(name) | salary |
+--------------------+------------+
| wukong | 1000000.31 |
| tianchi | 30000.00 |
| 程咬金 | 20000.00 |
+--------------------+------------+
sql语句的执行过程:
找到表 -> 拿着where指定的约束条件,去表中取出一条条记录 -> 将取出的一条条记录进行group by分组, 如果没有group by,则整体作为一组
-> 将分组的结果进行having过滤 -> 执行select -> 去重 -> 将结果按条件排序order by -> limit限制结果的显示条数
3.准备公司员工表
company.employee(公司.雇员)
员工id id int
姓名 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 primary key 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
depart_id int
);
插入记录
insert into employee(name ,sex,age,hire_date,post,salary,office,depart_id) values
('bajie','male',18,'20170301','visitor',7300.33,401,1), #以下是教学部
('wukong','male',78,'20150302','teacher',1000000.31,401,1),
('datang','male',81,'20130305','teacher',8300,401,1),
('shaseng','male',73,'20140701','teacher',3500,401,1),
('bailong','male',28,'20121101','teacher',2100,401,1),
('xizi','female',18,'20110211','teacher',9000,401,1),
('tianchi','male',18,'19000301','teacher',30000,401,1),
('xingjun','male',48,'20101111','teacher',10000,401,1),
('嘻嘻','female',48,'20150311','sale',3000.13,402,2), #以下是销售部门
('呵呵','female',38,'20101101','sale',2000.35,402,2),
('嘚嘚','female',18,'20110312','sale',1000.37,402,2),
('嘞嘞','female',18,'20160513','sale',3000.29,402,2),
('呢呢','female',28,'20170127','sale',4000.33,402,2),
('程咬氢','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)
;
查看表
> select * from employee;
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
| 1 | bajie | male | 18 | 2017-03-01 | visitor | NULL | 7300.33 | 401 | 1 |
| 2 | wukong | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 3 | datang | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 4 | shaseng | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 5 | bailong | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 6 | xizi | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 7 | tianchi | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 8 | xingjun | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 9 | 嘻嘻 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 10 | 呵呵 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 11 | 嘚嘚 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 12 | 嘞嘞 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 13 | 呢呢 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 14 | 程咬氢 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
+----+-----------+--------+-----+------------+-----------+--------------+------------+--------+-----------+
4.where约束
where字句中可以使用
比较运算符: > < >= <= = != <>
between 80 and 100: 值在80到100之间
in(10,20,30): 值是10或20或30
like '_bajie%': _代表一个字符, %号代表任意多个
逻辑运算符: not and or
代码:
> select * from employee where age in (18,28,38);
> select * from employee where name like 'x%'; #隐含条件: x前面没有通配符就是以 x 开头, 若后面也没有就是以什么结尾
5.group by
注意:
当有where时, 分组要放在where的后面.
分组指的是:
分组是按字段进行分组的
分组的作用
取每个部门的员工数 #'每'这个字后面的字段,就是我们分组的依据
取男女的数量
取最高,最低工资
> select * from employee group by post; #确实是按字段进行分组了, 但是得到的是每个分组里只有第一条数据展示了, 因为你使用了 * 查询, 其实这样是没有意义的(自己体会下)
> set global sql_mode='only_full_group_by'; #重启会话后生效: 如果要想分组查询, 这个必须设置, 正常应写到配置文件中(这样你在用 * 就直接报错)
> select @@global.sql_mode; #与select @@sql_mode; 一样
> select post from employee group by post; #根据哪个字段分组的, 只能查哪个字段, 其他字段不行: 而且查出来的只有分组的名字,若想查其他字段信息要通过'聚合函数'查询
#查其他字段的值: 聚合函数:group_concat(sex),用 ,号分隔连接展示
> select count(id),post from employee group by post;
> select sum(salary),post from employee group by post; #聚合函数: group_concat() count() sum() max() min() avg()
> select count(1),sex from employee group by sex; # 1 是什么, 为了优化性能, 隐含字段, 每条记录这个字段的值都是1
> select count(1) as '人数',sex as '性别' from employee group by sex; # 给查询的字段,显示的时候,起一个别名
五.可视化工具navicat的使用
下载地址:
内容总结
1.外键的变种 表和表之间的关系
一对多或多对一
多对多: 使用第三张表建立关系
一对一
2.数据驱动视图: Data Controller View: mysql python服务器 网页展示 (data model)
3.设计模式:26种
MVC
MTV
MVVM
4.单表查询
关键字的优先级
where
group by
having
select
destict
order by
limit
where
< > <= => = != <>
between .. and ..
in(1,2,3)
not and or
group by
sql_mode = only_full_group_by
只能获取分组的字段, 其他用聚合函数: count(1) sum() avg() max() min() group_concat()函数