table of Contents

First, the operation of the library

(A) by create

create database 数据库名称 charset utf8;
# 命名规范
#   1. 可以有字母、数字、下划线、@、#、$
#   2. 区分大小写
#   3. 唯一性
#   4. 不能使用关键字
#   5. 不能单独使用数字
#   6. 最长128位

(B) delete drop

drop database 数据库名称;

(Iii) changes alter charset

# 删除在增加
# 如果数据库中有数据的话，直接drop会导致数据库的数据丢失
# 线上环境，不能直接删除数据，在删除之前，需要进行备份
alter database 数据库名称 charset utf8 # 修改库的编码

(D) the investigation show

show databases;  #查看当前所有库
show create database 数据库名;  # 展示单个库
select database(); # 查看当前所在库

(5) the database use

use 数据库名; # 切换到库目录

Second, the operating table

(A) integrity constraint

auto_increment: Constraints field is the automatic growth 1
primary key: a unique identifier that is bound, column values can not be repeated, is equivalent to the primary key index, speed up queries
unsigned: Default Type range of signed numbers (with negative numbers), unsigned its constraint (not negative)
not null: identify the field can not be empty
default: specify default values, when the insert data, if not set, the default value is automatically added
zerofill: filled with 0s
foreign key: foreign key, you use the multi-table creation
unique: a unique identifier for multi-table created in one

# 例子1：
create table t2 (
id int auto_increment primary key,
name char(10)
)charset=utf8;

# 例子2：
create table t3 (
id int unsigned auto_increment primary key,
name char(10) not null default 'xxxx',
age int not null default 0
)charset-utf8;

(Ii) Data Types

Digital Type
- Integer type
  
  tinyint, smallint, mediumint, int, bigint is an integer type, commonly used int.
- Float
  1. float[m,d]: M represents a number of the total number, the maximum value of 255, d is the number of decimal places, maximum 30, with the increase of the decimal precision becomes inaccurate,
  2. double[m,d]: M represents a number of the total number, the maximum value of 255, d is the number of decimal places, the maximum value of 30, the accuracy is higher than the float, but it is not accurate
  3. decimal[m,d]: M represents the total number of digits, the maximum value of 65, d is the number of decimal places, maximum 30, with the increase of the decimal precision always accurate
```
# 例子1 ：
create table t5(
id int auto_increment primary key,
salary decimal(16,10),
num float
)charset=utf8;

# 例子2(刚好10位) ：
insert into t5 (salary, num) values(500023.2312345678, 5000.2374837284783274832);

# 例子3 （少于10位）
insert into t5(salary,num) values (500023.231234567, 5000.2374837284783274832);

# 例子4 （多于10位）
insert into t5 (salary,num) values (500023.23123456789, 5000.2374837284783274832);
```
String
1. char (length): length, in the range of (0-255)
  
  No matter how many characters are inserted, forever fixed duty prescribed length (will be filled with spaces), trailing spaces will be deleted when retrieving
  
  Scenario: ID card, phone number, MD5 encrypted value
2. varchar (length): variable length, range (0-65535)
  
  Is calculated according to the number of bytes occupied by the inserted length of the string will increase to hold a prefix byte size of the string
  
  Note: If you can not determine the insert size of the data is generally recommended to use varchar (255)
```
create table t6(
id int unsigned auto_increment primary key,
name char(10) not null default 'xxx',
)charset=utf8;

insert into t6 (name) values ('hello')  # 只能输入10个字节以内

insert into t6(name) values ('sadfasdfsafafdsadfdasf')  # 报错，超出范围
```

The date and time type

year
date
time
datetime
timestamp

General use datetime

create table t8(
d date,
t time,
dt datetime
);

select * from t8;

Enumeration and collection

enum: radio, only a selected value within a given range, such as gender
set: multiple choice, you can select one or more values within a given range (hobby)

create table t9(
id int auto_increment primary key,
gender enum('male','female')
)charset=utf8;

insert into t9 (gender) values('male');

inser into t9 (gender) values ('female')l

insert into t9(gender) values ('sdfasf0')  # 报错

(C) increase

(1) increasing the table create

# []内不是必填内容
create table 表名(
字段名 列类型 [约束条件]，  # 记住加逗号
····
字段名 列类型 [约束条件]   #最后一行不加逗号
）charset=utf8;  # 加分号


# 例子
#创建编码为utf8，字段为id、name的表t1
create table t1(  
id int,  
name char(5)
)charset=utf8;  

# 增加数据
insert into t1 (id,name) values (1,'wick');

# 查询数据
select * from t1;  # *代表查询所有的列

(2) increase the field alter add

The last one is added by default

alter table 表名
add 字段名 列类型 [约束条件],
add 字段名 列类型 [约束条件];

# 默认添加在最后一列之后
alter table t88 
add name varchar(32) not null default '';

Add in the first column (first)

alter table 表名
add 字段名 列类型 [约束条件] first;

# 添加在首行
alter table t88 
add name3 varchar(32) not null default '' first;

Add in the specified location (after)

alter table 表名
add 字段名 列类型 [约束条件] after 字段名;

# 添加在首行
alter table t88 
add name3 varchar(32) not null default '' after d;

(Iv) change

(1) modify the table name alter rename

alter table 旧表名 rename 新表名;

# 指令
alter table t8 rename t88;

(2) modify the field

1. modify

# 只可以修改字段的类型和约束条件
alter table 表名 modify 字段名 类型 [约束条件]

# 例子
alter table t88 modify name2 char(20);

2. change

# 可以修改字段、类型、约束条件
alter table 表名 change 旧字段名 新字段名 新数据类型 [约束条件]

# 例子
alter table t88 change name2 name22 varchar(32) not null default '';

alter table t88 change name22 name23;

(E) delete

Disable online

(1) Delete table drop

drop table 表名 

# 例子：
drop table t9;

(2) remove fields alter drop

alter table 表名 drop 字段名;

# 例子
alter table t88 drop name4;

(Vi) investigation show

show tables;: View all the current library table

show create table 表名;: View the table creation statements

(Vii) to copy the table structure create like

View the table creation statement, copy, run
```
show create table t88;
```
like to achieve

create table 新表名 like 旧表名;
```
create table t89 like t88;
```

Third, the operation record table

(A) by insert into

insert into 表名(列1,列2) values(值1,值2);

# 例子
insert into t1(id,name) values(1,'nick');

insert into t1(id,name) values(1,'tank'),(3,'zekai');

(B) check select from

(1) where conditions

Comparison operators:> <> = <= <> =!
between 80 and 100: 80 and 100 between, closed interval, comprising 80 and 100
in (23,45,23): the value is 23 or 45 or 23
like'wick% ': at the beginning of the wick,% represents any number of characters, a character logo _
Logical operators: and or not

select 列1 , 列2 from 表名; 
select * from 表名;  # 代表所有的列

# 例子
select * from t66 where id>30 and id<40;

select * from t66 where id between 31 and 33;

select * from t66 where id in (23,34,11);

select * from t66 where name like 'x%';  # x开头的
select * from t66 where name like '%x';  # x结尾的
select * from t66 where name like '%x%';  # 包含x的，不要用

# distinct避免重复 
select distinct name from t66;

# 四则运算，不要用
select name, age*10 from t3;

(C) delete delete, truncate

delete from 表名;  #删除表中所有数据
delete from 表名 where 条件;
truncate 表名;  # 没有where文件的，

# 例子
delete from t5 where id=1;
delete from t5 where id>=1;
delete from t5 where id>=1 and id<10;

truncate and delete differences:

After deleting delete, insert data from a primary key plus 1., starting from 1 TRUNCATE
delete to delete the equivalent line by line, truncate equivalent to select all to delete

(Iv) change update set

update 表名 set 列名1= 新值1，列名2=新值2 where 条件;

# 例子
uodate t66 set name = 'xxxx' where id = 30;

update t66 set name='xxxx' where id>20 or name='zekai';

supplement

sql command must be added;
tee D:/mylog.log: Automatically to the next all the sql statements and results into file

Second, databases, tables, records of operation