数据库

将sid字段修改为id并且加上了自增长约束","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"C0hl-1659669495422","name":"paragraph","data":{},"nodes":[{"type":"text","id":"AbAM-1659669495420","leaves":[{"text":"alter  table  tb_user  add  id2  int(10);  ==>添加id2这个字段","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"NgpI-1659669750816","name":"paragraph","data":{},"nodes":[{"type":"text","id":"mgsY-1659669750813","leaves":[{"text":"alter  table  tb_ user add（id3  int（10），id4  int（10））；     ==》同时添加2个字段","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"pWC2-1659670213122","name":"paragraph","data":{},"nodes":[{"type":"text","id":"ZjBE-1659670213120","leaves":[{"text":"alter table tb_user add id5  int(10)first； ==》 把id5字段放到最前面","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"H7BR-1659670366896","name":"paragraph","data":{},"nodes":[{"type":"text","id":"OFjP-1659670366894","leaves":[{"text":"alter  table  tb_user  add  id6  int（10）after  phone；  ==》把id6这个字段放到phone字段后","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"Yd5I-1659670580134","name":"paragraph","data":{},"nodes":[{"type":"text","id":"f0c2-1659670580133","leaves":[{"text":"alter  table  tb_user  drop  id5；==》删除id5字段","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"jdFj-1659670655534","name":"paragraph","data":{},"nodes":[{"type":"text","id":"aVFL-1659670655532","leaves":[{"text":"alter  table  tb_user  drop   id2，drop  id3，drop  id4；  ==》同时删除多个字段","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"BK9E-1659670801976","name":"paragraph","data":{},"nodes":[{"type":"text","id":"hEc7-1659670801974","leaves":[{"text":"drop  table  tb_user；  ==》删除tb_user表","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"},{"type":"color","value":"#CC0000"}]}]}],"state":{}},{"type":"block","id":"V2dH-1659679849537","name":"paragraph","data":{},"nodes":[{"type":"text","id":"xTAb-1659679849535","leaves":[{"text":"{对表数据的操作}","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"},{"type":"color","value":"#CC0000"}]}]}],"state":{}},{"type":"block","id":"ZAQe-1659679934168","name":"paragraph","data":{},"nodes":[{"type":"text","id":"yzzS-1659679934166","leaves":[{"text":"增 ==》insert  into","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"},{"type":"color","value":"#CC0000"}]}]}],"state":{}},{"type":"block","id":"0CrX-1659681278746","name":"paragraph","data":{},"nodes":[{"type":"text","id":"H2Mk-1659681278744","leaves":[{"text":"insert   into  tb_user(id，name，class，phone)values(1，" xiaowang'，1001，13533333333）；","marks":[{"type":"fontsize","value":18},{"type":"fontfamily","value":"arial="" black"}]}]}],"state":{}},{"type":"block","id":"bnx3-1659681675071","name":"paragraph","data":{},"nodes":[{"type":"text","id":"ucz1-1659681675070","leaves":[{"text":"insert="" into="" tb_user="" values(2，‘xiaowang’，1002，1354444444）；","marks":[{"type":"fontsize","value":18},{"type":"fontfamily","value":"arial="" black"}]}]}],"state":{}},{"type":"block","id":"frb9-1659683435169","name":"paragraph","data":{},"nodes":[{"type":"text","id":"1y6e-1659683435166","leaves":[{"text":"insert="" tb_user(name)values('xiaoliu');="=">给指定字段插入数据","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"fzjq-1659683674348","name":"paragraph","data":{},"nodes":[{"type":"text","id":"FcaC-1659683674346","leaves":[{"text":" insert  into tb_user（name，class）values（‘xiaoliu’，1001）；  ==》给指定字段一次插入多条数据","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"FHYp-1659683838904","name":"paragraph","data":{},"nodes":[{"type":"text","id":"xa6A-1659683838902","leaves":[{"text":"null  不等于0，null是指空的属性   0是代表一个值","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"LbcA-1659681648392","name":"paragraph","data":{},"nodes":[{"type":"text","id":"K39f-1659681648389","leaves":[{"text":"  ","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"NyYx-1659679939880","name":"paragraph","data":{},"nodes":[{"type":"text","id":"107I-1659679939879","leaves":[{"text":"查","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"},{"type":"color","value":"#CC0000"}]}]}],"state":{}},{"type":"block","id":"hNco-1659683895772","name":"paragraph","data":{},"nodes":[{"type":"text","id":"LGXc-1659683895769","leaves":[{"text":"select * from tb_user；  ==》查询表中所有数据","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"},{"type":"color","value":"#CC0000"}]}]}],"state":{}},{"type":"block","id":"cedI-1659684002385","name":"paragraph","data":{},"nodes":[{"type":"text","id":"lglC-1659684002383","leaves":[{"text":"select * from tb_user  where  class=1001； ==》查询class为1001的所有数据","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"VmXW-1659684079635","name":"paragraph","data":{},"nodes":[{"type":"text","id":"A7Kc-1659684079633","leaves":[{"text":"select  name  from tb_user  where  class=1001；==》查询单个字段","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"PVWy-1659684210815","name":"paragraph","data":{},"nodes":[{"type":"text","id":"pDRB-1659684210813","leaves":[{"text":"select  name ，class  from tb_user  where  class=1001； ==》查询多个字段","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"3HRP-1659679945416","name":"paragraph","data":{},"nodes":[{"type":"text","id":"TMCu-1659679945414","leaves":[{"text":"改","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"},{"type":"color","value":"#CC0000"}]}]}],"state":{}},{"type":"block","id":"laa1-1659684266519","name":"paragraph","data":{},"nodes":[{"type":"text","id":"y4aJ-1659684266517","leaves":[{"text":"update  +表名 set 字段名=值  where 条件","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"},{"type":"color","value":"#CC0000"}]}]}],"state":{}},{"type":"block","id":"P5Uu-1659684331260","name":"paragraph","data":{},"nodes":[{"type":"text","id":"VZlM-1659684331258","leaves":[{"text":"update tb_user  set  phone=18888888888  where name='xiaozhao';","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"zChQ-1659684421761","name":"paragraph","data":{},"nodes":[{"type":"text","id":"MS5x-1659684421758","leaves":[{"text":"==>修改name为xiaozhao的数据","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"WNo8-1659684528147","name":"paragraph","data":{},"nodes":[{"type":"text","id":"BQ5m-1659684528144","leaves":[{"text":"update tb_user  set  phone=12344444444  where  id=7；","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"5KVY-1659684569433","name":"paragraph","data":{},"nodes":[{"type":"text","id":"Oqpi-1659684569430","leaves":[{"text":"==》修改id等于7的数据","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"T2jF-1659679956622","name":"paragraph","data":{},"nodes":[{"type":"text","id":"0PAl-1659679956620","leaves":[{"text":"删","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"},{"type":"color","value":"#CC0000"}]}]}],"state":{}},{"type":"block","id":"aySL-1659670550501","name":"paragraph","data":{},"nodes":[{"type":"text","id":"vSWd-1659670550499","leaves":[{"text":"delete from +表名 where 条件","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"},{"type":"color","value":"#CC0000"}]}]}],"state":{}},{"type":"block","id":"Gy1K-1659684667514","name":"paragraph","data":{},"nodes":[{"type":"text","id":"dci8-1659684667512","leaves":[{"text":"delete from tb_user  where  id=7;  ==>删除id等于7的数据","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"B7HL-1659684734040","name":"paragraph","data":{},"nodes":[{"type":"text","id":"9nba-1659684734038","leaves":[{"text":"delete from tb_user ；  ==》删除全表数据,表结构在","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"P4uB-1659684770606","name":"paragraph","data":{},"nodes":[{"type":"text","id":"bIqk-1659684770605","leaves":[{"text":"truncate tb_user;  ==>删除全表数据","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}},{"type":"block","id":"GwVy-1659684828492","name":"paragraph","data":{},"nodes":[{"type":"text","id":"OdZg-1659684828491","leaves":[{"text":"drop  table tb_user;  ==>删除表结构和表数据","marks":[{"type":"fontSize","value":18},{"type":"fontFamily","value":"Arial Black"}]}]}],"state":{}}]'>show  databases；   ==》查看所有的库
创建数据库：create  database  库名称
create  database dcs18；   ==》创建名称叫dcs18的库
use dcs18；  ==》 进入dcs18这个库
show  tables；   ==》查看当前所在库下的所有表
select database（）；   ==》查看当前已经进入到哪个库里面
drop database  dcs18；  ==》删除dcs18这个库
新建一个user表
create table user(id int(5)primary key auto_increment,name varchar(10)not null,class int(10),phone bigint(20)default"13311111111");
数据类型：
int   ==》整数，最大存储值为2147483647
bigint  ==》存储手机号
varchar  ==》存字符串（存的数据需要加单引号或双引号）
date  ==》时间  如“2022-08-05”
float   ==》小数
约束
not  null  ==》非空约束
primary  key  ==》主键约束，里面的值是唯一的不能重复
auto increment   ==》自增长约束
foregin  key  ==》 外键约束
{对表结构修改}
desc  user   查看表结构
修改表名
alter table  +表名  rename  +新表名
alter  table  user  rename tb_user;   ==》将user表名修改为tb_user;
alter  table  tb_user  change  id  sid  int(10);   ==》将id字段修改为sic并且去掉自增长约束
alter  table user change  sid id  int（5）auto_increment;   ==>将sid字段修改为id并且加上了自增长约束
alter  table  tb_user  add  id2  int(10);  ==>添加id2这个字段
alter  table  tb_ user add（id3  int（10），id4  int（10））；     ==》同时添加2个字段
alter table tb_user add id5  int(10)first； ==》 把id5字段放到最前面
alter  table  tb_user  add  id6  int（10）after  phone；  ==》把id6这个字段放到phone字段后
alter  table  tb_user  drop  id5；==》删除id5字段
alter  table  tb_user  drop   id2，drop  id3，drop  id4；  ==》同时删除多个字段
drop  table  tb_user；  ==》删除tb_user表
{对表数据的操作}
增 ==》insert  into
insert   into  tb_user(id，name，class，phone)values(1，'xiaowang'，1001，13533333333）；
insert  into  tb_user  values(2，‘xiaowang’，1002，1354444444）；
insert  into tb_user(name)values('xiaoliu');   ==>给指定字段插入数据
insert  into tb_user（name，class）values（‘xiaoliu’，1001）；  ==》给指定字段一次插入多条数据
null  不等于0，null是指空的属性   0是代表一个值
  
查
select * from tb_user；  ==》查询表中所有数据
select * from tb_user  where  class=1001； ==》查询class为1001的所有数据
select  name  from tb_user  where  class=1001；==》查询单个字段
select  name ，class  from tb_user  where  class=1001； ==》查询多个字段
改
update  +表名 set 字段名=值  where 条件
update tb_user  set  phone=18888888888  where name='xiaozhao';
==>修改name为xiaozhao的数据
update tb_user  set  phone=12344444444  where  id=7；
==》修改id等于7的数据
删
delete from +表名 where 条件
delete from tb_user  where  id=7;  ==>删除id等于7的数据
delete from tb_user ；  ==》删除全表数据,表结构在
truncate tb_user;  ==>删除全表数据
drop  table tb_user;  ==>删除表结构和表数据