标签：有关 err XML 电话号码 别名 多对多 第三范式 from 注意
放在内存里——瞬时：程序结束，上次的数据就没啦
不安全
不方便在中间插入、删除数据
但也不是一无是处，可以应用于配置文件：.xml文件、.ini文件等等
核心：CRUD（最难的是“查找”）
层次模型
优点：层次清晰
缺点：（假如一张“专业”表有你，“学校”表也有你）
查询效率低下（不知道查哪张）
数据不完整（这张表改了那张表没改）
致命：重复就GG了
网状模型
优点：解决复杂问题，数据也完整了，重复的话也只操作一个文件
缺点：重复文件没法解决特殊性问题（假设计算机一班的人和上mysql课的有一部分人都是）
计算机一班的每人收100元
上mysql课的每人收233元
致命：并未解决导航问题
关系型
解决了导航问题：比如每张表都有个学号（公共的编号）
分批管理，各管各的
数据完整，层次清晰
说白了，关系就是共性，为了让每张表都能找到爹
**和谁都有关系，但是又互不影响
CRUD：增删改查（查找是最难的）
创建数据库：
create database if not exists `student`;
删除数据库：
drop database if exists student;
查看创建的数据库：
show create database `teacher`;
乱码->字符编码：GBK、UTF-8(在学习中用GBK，企业中UTF-8)
create database if not exists `student` charset=gbk;
修改、更新数据库字符编码：
alter database teacher charset=gbk;
使用数据库 -> 创建表
使用数据库(use + 数据库名)：
use frank_school;
查看表：
show tables;
创建表：
create table student(
id int,
name varchar(30),
age int
);
创建表（B格）：
create table teacher(
id int auto_increment primary key comment ‘主键id‘,
#auto_increment 自动增长
#primary key 主键，最主要的，用来区分
#comment 注释
name varchar(30) not null,
#not null 不能为空
phone varchar(20) comment ‘电话号码‘,
address varchar(100) default ‘暂时未知‘ comment ‘住址‘
#default 默认值，此处为‘暂时未知‘
)engine=innodb;
查看表的结构：
desc student; desc teacher;
删除表：
drop table if exists oooo, stu,jjj;
修改表：
添加字段：
#默认在最后面 alter table student add phone varchar(20); #指定插入在哪，在name前面 alter table student add phone varchar(20) after name; #在最前面 alter table student add phone varchar(20) first;
删除字段：
drop table s; alter table student drop address;in
修改字段：
#既可以修改名字，也可以修改类型 alter table student change phone tel_phone int (11); #只改变类型 alter table student modify tel_phone int (13);
插入数据
insert into teacher (id, name, phone, address) values(1, ‘Frank‘, ‘1888888‘, ‘ShangHai‘); # 这样就必须按照创建表的时候的顺序填写 insert into teacher values(1, ‘Frank‘, ‘1888888‘, ‘ShangHai‘);
查看数据
select * from teacher; # *:全部 # from + 表
删除数据
# 删除id为6的数据 delete from teacher where id=6; # 删除大于三十岁的数据 delete from student where age>30; # 清除表的所有数据（不建议:慢） # 坏处：再创建数据的时候，id等自增数据，会接着被清空之前的id自动增长 delete from teacher; # 建议这种方法清除数据 # 好处：id等自增数据，不会接着被清空之前的id truncate table student;
更新数据
# 将id=1的name，改为frank # 注意where后面的，注意不要有重复的id等！！！！ update teacher set name=‘frank‘ where id=1; # 也可以改多个数据 update teacher set name=‘frank‘,phone=‘1111‘ where id=1; # 如果不写where，那么将改变所有的数据 update teacher set name=‘frank‘; # SQL注入攻击就是改变where # 多个条件的情况 # 将phone为1111111或者2222的数据修改address的值 update teacher set address=‘shanghai‘ where phone=‘1111111‘ or phone=‘2222‘;
查询表数据
# 查询teacher表中的id跟phone的数据 select id,phone from teacher; # 查询teacher表中所有的数据 select * from teacher;
DDL：data definition language 数据库定义语言（create、alter、drop、show...)
DML：data manipulation language 数据操纵语言（insert、update、select...)
DCL： data control language
查找所有字符集设置
show variables like ‘character_set_%‘;
设置客户端字符集
set character_set_client=utf8;
auto_increment自增属性一定是主键
auto_increment的属性中，删除id=3的数据后，就不能再插入一个id为3的数据了
删除主键：
alter table t_8 drop primary key;
unique唯一键添加：
create table t_9( id int primary key, phone varchar(20) unique );
两个unique唯一键：
create table t_11( id int, name varchar(20) unique, phone varchar(20) unique );
删除唯一键：
alter table t_11 drop index phone; // 执行后，phone不是唯一键了
主键与唯一键的区别：
主键不能重复，不能空
；唯一键也可以重复，可以为空；
sql内注释和代码注释：
create table t_12( id int(20), name varchar(20) comment ‘姓名‘ ); // comment注释 show create table t_12; // 会显示怎么创建的，包括注释都可以看到
数据库完整性：
要有一个主键，自动增长；
有些要有default，暂无，例子：有同学考试缺考，就要用default
外键：用于连接两个表，
create table eatery( id int primary key, money decimal(10,4), stuId int(4), foreign key (stuId) references stu(stuId) ); // 从stu表中的stuId创建外键
显示表怎么创建的：
show create table eatery;
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table
|
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| eatery | CREATE TABLE `eatery` (
`id` int(11) NOT NULL,
`money` decimal(10,4) DEFAULT NULL,
`stuId` int(4) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `stuId` (`stuId`),
CONSTRAINT `eatery_ibfk_1` FOREIGN KEY (`stuId`) REFERENCES `stu` (`stuId`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk |
+--------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.04 sec)
删除外键
alter table eatery drop foreign key eatery_ibfk_1;
置空：删除数据（只更删除几个）
级联：更新数据（操作的是所有的数据）
// 创建主表
create table stu(
-> stuId int(4) primary key,
-> name varchar(20)
-> );
// 创建从表
create table eatery(
-> id int (4) primary key,
-> money decimal(10,4),
-> stuId int(4),
-> foreign key(stuId) references stu(stuId) on delete set null on update cascade
// on delete set null：当删除时，置空
// on update cascade：当更新时，级联
-> );
关系：关系型数据库，有两张表的共有字段去确定数据的完整性
行：一条数据，一条数据记录，实体
列：一个字段，属性
一对一，一对多，多对一，多对多
第一范式 确保每列原子性
第二范式 非键字段必须依赖键字段
第三范式 消除传递依赖
select
mysql> select 3*4; +-----+ | 3*4 | +-----+ | 12 | +-----+ 1 row in set (0.00 sec) // 起“别名” mysql> select 2*6 as res; +-----+ | res | +-----+ | 12 | +-----+ 1 row in set (0.00 sec)
from
mysql> select * from t1; +------+-------+ | id | name | +------+-------+ | 1 | frank | | 2 | jerry | +------+-------+ 2 rows in set (0.00 sec) mysql> select * from t2; +--------+--------+ | score1 | score2 | +--------+--------+ | 98 | 99 | | 90 | 77 | +--------+--------+ 2 rows in set (0.00 sec) mysql> select * from t1,t2; // 返回笛卡尔积 +------+-------+--------+--------+ | id | name | score1 | score2 | +------+-------+--------+--------+ | 1 | frank | 98 | 99 | | 2 | jerry | 98 | 99 | | 1 | frank | 90 | 77 | | 2 | jerry | 90 | 77 | +------+-------+--------+--------+ 4 rows in set (0.00 sec)
where
mysql> select * from t4; +------+----------+ | id | address | +------+----------+ | 1 | shanghai | | 2 | shanghai | | 3 | beijing | | 4 | shenzhen | +------+----------+ 4 rows in set (0.00 sec) // where限定查找某一个范围 mysql> select * from t4 where address = ‘shanghai‘; +------+----------+ | id | address | +------+----------+ | 1 | shanghai | | 2 | shanghai | +------+----------+ 2 rows in set (0.00 sec) mysql> select * from t4 where address = ‘shenzhen‘; +------+----------+ | id | address | +------+----------+ | 4 | shenzhen | +------+----------+ 1 row in set (0.00 sec) mysql> select * from t4 where address = ‘shenzhen ‘; +------+----------+ | id | address | +------+----------+ | 4 | shenzhen | +------+----------+ 1 row in set (0.00 sec)
in
// 跟or一样 mysql> select * from t4 where address in(‘beijing‘,‘shanghai‘); +------+----------+ | id | address | +------+----------+ | 1 | shanghai | | 2 | shanghai | | 3 | beijing | +------+----------+ 3 rows in set (0.00 sec)
between...and...
mysql> select * from t3 where age between 15 and 19; +------+------+ | id | age | +------+------+ | 1 | 18 | | 2 | 19 | | 3 | 19 | | 4 | 16 | | 5 | 17 | +------+------+ 5 rows in set (0.00 sec)
is null
// 查找为空的 // is not null mysql> select * from t3 where age is null; +------+------+ | id | age | +------+------+ | 7 | NULL | +------+------+ 1 row in set (0.00 sec)
聚合函数
mysql> select * from score; +------+---------+---------+------+ | id | chinese | english | math | +------+---------+---------+------+ | 1 | 98 | 99 | 100 | | 2 | 90 | 95 | 85 | +------+---------+---------+------+ 2 rows in set (0.00 sec) // 求和 mysql> select sum(chinese) from score; +--------------+ | sum(chinese) | +--------------+ | 188 | +--------------+ 1 row in set (0.00 sec) // 平均值 mysql> select avg(chinese) from score; +--------------+ | avg(chinese) | +--------------+ | 94.0000 | +--------------+ 1 row in set (0.00 sec) // 最大值 mysql> select max(chinese) from score; +--------------+ | max(chinese) | +--------------+ | 98 | +--------------+ 1 row in set (0.00 sec) // 最小值 mysql> select min(chinese) from score; +--------------+ | min(chinese) | +--------------+ | 90 | +--------------+ 1 row in set (0.00 sec) // 求数量（很坑，不建议用） mysql> select count(*) from score; +----------+ | count(*) | +----------+ | 2 | +----------+ 1 row in set (0.00 sec)
like模糊查询
mysql> select * from student; +------+--------+--------+------+-----------+ | id | name | gender | age | tel_phone | +------+--------+--------+------+-----------+ | 1 | 张三 | 0 | 18 | 155555 | | 2 | 张四 | 1 | 20 | 16541654 | | 3 | 李四 | 1 | 22 | 1231 | | 4 | 张某某 | 0 | 15 | 15646 | +------+--------+--------+------+-----------+ 4 rows in set (0.00 sec) // %代表多个字符 mysql> select * from student where name like ‘张%‘; +------+--------+--------+------+-----------+ | id | name | gender | age | tel_phone | +------+--------+--------+------+-----------+ | 1 | 张三 | 0 | 18 | 155555 | | 2 | 张四 | 1 | 20 | 16541654 | | 4 | 张某某 | 0 | 15 | 15646 | +------+--------+--------+------+-----------+ 3 rows in set (0.00 sec) // _代表一个字符 mysql> select * from student where name like ‘张_‘; +------+------+--------+------+-----------+ | id | name | gender | age | tel_phone | +------+------+--------+------+-----------+ | 1 | 张三 | 0 | 18 | 155555 | | 2 | 张四 | 1 | 20 | 16541654 | +------+------+--------+------+-----------+ 2 rows in set (0.00 sec)
order by 排序查询
mysql> select * from score; +------+---------+---------+------+ | id | chinese | english | math | +------+---------+---------+------+ | 1 | 98 | 99 | 100 | | 2 | 90 | 95 | 85 | | 3 | 87 | 79 | 99 | +------+---------+---------+------+ 3 rows in set (0.00 sec) // asc升序 mysql> select * from score order by english asc; +------+---------+---------+------+ | id | chinese | english | math | +------+---------+---------+------+ | 3 | 87 | 79 | 99 | | 2 | 90 | 95 | 85 | | 1 | 98 | 99 | 100 | +------+---------+---------+------+ 3 rows in set (0.00 sec) // desc降序 mysql> select * from score order by english desc; +------+---------+---------+------+ | id | chinese | english | math | +------+---------+---------+------+ | 1 | 98 | 99 | 100 | | 2 | 90 | 95 | 85 | | 3 | 87 | 79 | 99 | +------+---------+---------+------+ 3 rows in set (0.00 sec)
group by 分组查询
mysql> select * from info; +----+------+--------+---------+ | id | age | gender | address | +----+------+--------+---------+ | 1 | 25 | 男 | 上海 | | 2 | 23 | 女 | 上海 | | 3 | 24 | 女 | 北京 | | 4 | 26 | 男 | 北京 | | 5 | 22 | 男 | 上海 | +----+------+--------+---------+ 5 rows in set (0.00 sec) // 按照性别分组统计平均年龄 // 1.可以分组2.聚合函数 mysql> select avg(age) as ‘年龄‘,gender as ‘性别‘ from info group by gender; +---------+------+ | 年龄 | 性别 | +---------+------+ | 24.3333 | 男 | | 23.5000 | 女 | +---------+------+ 2 rows in set (0.00 sec)
group_concat
mysql> select * from student; +----+------+-------+--------+---------+ | id | age | name | gender | phone | +----+------+-------+--------+---------+ | 1 | 18 | ???? | 0 | 115555 | | 2 | 20 | ?? | 1 | 5621654 | | 3 | 31 | ????? | 1 | 15646 | | 4 | 32 | ?? | 1 | 4856748 | +----+------+-------+--------+---------+ 4 rows in set (0.00 sec) // 根据gender将id分组，进行聚合显示 mysql> select group_concat(id),gender from student group by gender; +------------------+--------+ | group_concat(id) | gender | +------------------+--------+ | 1 | 0 | | 2,3,4 | 1 | +------------------+--------+ 2 rows in set (0.01 sec)
having
mysql> desc info; +---------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------+--------------+------+-----+---------+-------+ | id | int(11) | NO | PRI | NULL | | | age | int(11) | YES | | NULL | | | gender | varchar(5) | YES | | NULL | | | address | varchar(255) | YES | | NULL | | +---------+--------------+------+-----+---------+-------+ 4 rows in set (0.00 sec) // having是在查询之后的数据进行筛选（已经查询之后的） mysql> SELECT avg(age) AS ‘age‘,address AS ‘address‘ FROM info GROUP BY address HAVING age > 24; +---------+---------+ | age | address | +---------+---------+ | 24.5000 | beijing | +---------+---------+ 1 row in set (0.00 sec)
limit
mysql> select * from info
-> ;
+----+------+--------+----------+
| id | age | gender | address |
+----+------+--------+----------+
| 1 | 25 | 0 | shanghai |
| 2 | 23 | 1 | shanghai |
| 3 | 26 | 1 | beijing |
| 4 | 23 | 0 | beijing |
| 5 | 21 | 0 | shanghai |
| 6 | 24 | 1 | shenzhen |
+----+------+--------+----------+
6 rows in set (0.00 sec)
// 从下标为0开始，查两个
mysql> select * from info limit 0,2;
+----+------+--------+----------+
| id | age | gender | address |
+----+------+--------+----------+
| 1 | 25 | 0 | shanghai |
| 2 | 23 | 1 | shanghai |
+----+------+--------+----------+
2 rows in set (0.00 sec)
// 降序前三个
mysql> select * from info order by age desc limit 3;
+----+------+--------+----------+
| id | age | gender | address |
+----+------+--------+----------+
| 3 | 26 | 1 | beijing |
| 1 | 25 | 0 | shanghai |
| 6 | 24 | 1 | shenzhen |
+----+------+--------+----------+
3 rows in set (0.00 sec)
distinct
mysql> select distinct address from info; +----------+ | address | +----------+ | shanghai | | beijing | | shenzhen | +----------+ 3 rows in set (0.00 sec) // 去除重复的，计算个数 mysql> select count(distinct address) from info; +-------------------------+ | count(distinct address) | +-------------------------+ | 3 | +-------------------------+ 1 row in set (0.00 sec)
union联合查询
mysql> select * from teacher; +------+------+--------+----------+ | id | age | gender | address | +------+------+--------+----------+ | 1 | 25 | 0 | shanghai | | 2 | 23 | 1 | shanghai | | 3 | 26 | 1 | beijing | | 4 | 23 | 0 | beijing | | 5 | 21 | 0 | shanghai | | 6 | 24 | 1 | shenzhen | +------+------+--------+----------+ 6 rows in set (0.00 sec) mysql> select * from info; +----+------+--------+----------+ | id | age | gender | address | +----+------+--------+----------+ | 1 | 25 | 0 | shanghai | | 2 | 23 | 1 | shanghai | | 3 | 26 | 1 | beijing | | 4 | 23 | 0 | beijing | | 5 | 21 | 0 | shanghai | | 6 | 24 | 1 | shenzhen | +----+------+--------+----------+ 6 rows in set (0.00 sec) mysql> select age,gender from info union select `name`,phone from student; +-------+---------+ | age | gender | +-------+---------+ | 25 | 0 | | 23 | 1 | | 26 | 1 | | 23 | 0 | | 21 | 0 | | 24 | 1 | | ???? | 115555 | | ?? | 5621654 | | ????? | 15646 | | ?? | 4856748 | +-------+---------+ 10 rows in set (0.00 sec)
inner join（内连接）
// 查name和score
mysql> select
name,
score
from
student
inner join score on student.id=score.stuid;
+----------+-------+
| name | score |
+----------+-------+
| zhangsan | 89.00 |
| ren | 80.00 |
| lalala | 70.00 |
+----------+-------+
3 rows in set (0.00 sec)
left join（左连接同理right join）
// 以左表为基准，该方式student为左表
mysql> select
-> name,
-> score
-> from
-> student left join score
-> on student.id = score.stuid;
+----------+-------+
| name | score |
+----------+-------+
| zhangsan | 89.00 |
| ren | 80.00 |
| lalala | 70.00 |
| moumou | NULL |
+----------+-------+
4 rows in set (0.00 sec)
cross join（两个表的笛卡尔积）
natural join：公共的字段，条件是有同名的字段，然后相当于将两个表内、左、右连接
若没有公共字段即同名的字段，则返回笛卡尔积
using：当两个表的字段完全相同，若内连接，则返回空，这就要用using指定字段
不推荐using和natural join，一般使用inner join
基本语句
mysql> select * from score; +----+-------+-------+ | id | stuid | score | +----+-------+-------+ | 1 | 1 | 89.00 | | 2 | 3 | 80.00 | | 3 | 4 | 70.00 | +----+-------+-------+ 3 rows in set (0.02 sec) // 多个结果要用in不用=，还有not in mysql> select * from student where id in (select stuid from score where score >= 75); +----+------+----------+--------+--------+ | id | age | name | gender | phone | +----+------+----------+--------+--------+ | 1 | 18 | zhangsan | 0 | 115555 | | 3 | 31 | ren | 1 | 15646 | +----+------+----------+--------+--------+ 2 rows in set (0.01 sec)
exists和not exists
mysql> select * from score; +----+-------+-------+ | id | stuid | score | +----+-------+-------+ | 1 | 1 | 89.00 | | 2 | 3 | 80.00 | | 3 | 4 | 70.00 | +----+-------+-------+ 3 rows in set (0.00 sec) mysql> select * from student where exists (select stuid from score where score >=85); +----+------+----------+--------+---------+ | id | age | name | gender | phone | +----+------+----------+--------+---------+ | 1 | 18 | zhangsan | 0 | 115555 | | 2 | 20 | moumou | 1 | 5621654 | | 3 | 31 | ren | 1 | 15646 | | 4 | 32 | lalala | 1 | 4856748 | +----+------+----------+--------+---------+ 4 rows in set (0.00 sec) mysql> select * from student where exists (select stuid from score where score >=100); Empty set (0.00 sec)
隐藏敏感的数据
降低sql语句的复杂度
创建
// 这样就可以只看到student的name和phone，而不用看到其他敏感的数据 create view vw_stu as select name,phone from student; // 保存视图之后，就可以直接查视图，而不用再把查询语句写一遍 select * from vw_stu;
显示视图
// 显示视图，所以必须要用前缀区分
mysql> show tables;
+------------------------+
| Tables_in_frank_school |
+------------------------+
| info |
| score |
| student |
| teacher |
| vw_stu |
+------------------------+
5 rows in set (0.00 sec)
mysql> desc vw_stu;
+-------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+-------+
| name | varchar(255) | YES | | NULL | |
| phone | varchar(20) | YES | | NULL | |
+-------+--------------+------+-----+---------+-------+
2 rows in set (0.00 sec)
mysql> show create view vw_stu;
+--------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| View | Create View
| character_set_client | collation_connection |
+--------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
| vw_stu | CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `vw_stu` AS select `student`.`name` AS `name`,`student`.`phone` AS `phone` from `student` | utf8mb4 | utf8mb4_general_ci
|
+--------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------+----------------------+
1 row in set (0.00 sec)
mysql> show table status where comment = ‘view‘ \G
*************************** 1. row ***************************
Name: vw_stu
Engine: NULL
Version: NULL
Row_format: NULL
Rows: NULL
Avg_row_length: NULL
Data_length: NULL
Max_data_length: NULL
Index_length: NULL
Data_free: NULL
Auto_increment: NULL
Create_time: NULL
Update_time: NULL
Check_time: NULL
Collation: NULL
Checksum: NULL
Create_options: NULL
Comment: VIEW
1 row in set (0.00 sec)
更新和删除视图
// 修改视图要查的东西 mysql> alter view vw_stu as select age,name,phone from student; Query OK, 0 rows affected (0.01 sec) // 删除 drop view vw_stu;
将子查询放到视图里的时候要特别注意，要将算法改为temptable
只要commit就不能再rollback了
标签：有关 err XML 电话号码 别名 多对多 第三范式 from 注意
原文地址：https://www.cnblogs.com/Angela-Joker/p/14602400.html
