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Table 1. Operation

increase

create table 表名(
    字段名 字段类型[字段约束]
    ....
)charset=utf8

Field Type

digital

Integer

tinyint
smallint
int     *********************
mediumint
bigint

区别 :
    取值的范围不一样
    加上unsigned,代表只能取整数

Float

float
double
decimal(10,5)

String type

char()  定长
    身份证,手机号
varchar()   变长
    哈希密码

区别:
    1.char(4)  'ab  ' 占4个字节,剩余的不足字节用空字节补充
    2.varchar(4) 'ab' 占3个字节,其中有两个是自身的大小,还有一个是记录字节的大小

Time Type

datetime**************

年月日时分秒

enumerate

enum
gender enum('male','female') default 'female';

Column constraint (optional parameters)

auto_increment  自增
not null    不能为null
primary key     主键索引
default     默认值

delete

drop table 表名;

Delete field name

alter table 表名 drop 字段名;

change

New table fields

alter table 表名 add 列声明;
alter table 表名 add 列声明 frist;
alter table 表名 add 列声明 after 字段名;

Field name changes to the table

alter table 表名 modify 字段名 字段类型[字段约束]
alter table 表名 change 旧字段 新字段 字段类型[字段约束];

check

show tables;

Operating data row

increase

insert into 表名(列1,列2) values(值1,值2),(值1,值2);

delete

delete from 表名;
    自增继续加1,一行行删除
truncate 表名;
    全选删除,自增键重新开始,速度快

Conditional deletion

delete from 表名 where id=10;
delete from 表名 where id=10 and name='n';

change

update 表名 set name='zekai',age=12;

Modified as conditions

update 表名 set name='zekai', age=15 where age=12 and num=10;

check

select * from 表名;   返回表中所有数据
select 列名1,列名2 from 表名;

Search by condition

select * from where id=10;

between...and...

select * from 表名 id between 30 and 40;

distinct deduplication

select distinct name from t6;

in query

select 

like fuzzy query

Arithmetic

is null

Table 1. Single Operation

Packet

All data packets are classified according to a same field

group by

order

limit

2. Multi-table operations

Foreign key

3.mysql backup

create table department(
                id int auto_increment primary key,
                name varchar(32) not null default ''
            )charset utf8;
            
            insert into department (name) values ('研发部');
            insert into department (name) values ('运维部');
            insert into department (name) values ('前台部');
            insert into department (name) values ('小卖部');
            
            create table userinfo (
                id int auto_increment primary key,
                name varchar(32) not null default '',
                depart_id int not null default 1,
                constraint fk_user_depart foreign key (depart_id) references department(id)
            )charset utf8;
            
            insert into userinfo (name, depart_id) values ('zekai', 1);
            insert into userinfo (name, depart_id) values ('xxx', 2);
            insert into userinfo (name, depart_id) values ('zekai1', 3);
            insert into userinfo (name, depart_id) values ('zekai2', 4);
            insert into userinfo (name, depart_id) values ('zekai3', 1);
            insert into userinfo (name, depart_id) values ('zekai4', 2);
            insert into userinfo (name, depart_id) values ('zekai4', 5);