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1.修改表名
alter table t1 rename t2;
2.修改表里字段類型
alter table t1 modify name char(5);
3.修改表里字段名
alter table t1 change name age int;
4.復制表
create table t2 like t1; 復制表的結構約束 無數據
create table t2 select *from t1; 復制表的數據與結構 無約束
create table t2 select*from t1 where 1=2(假命題) 復制表的結構
5.請空表
truncate 他
6.添加
alter table t1 add name char(5) not null first
alter table t1 add name char(5) not null after age
7.刪除字段名
alter table t1 drop name;
用戶管理
創建用戶
create user zero@localhost identified by'zero';
創建權限
grant all on db1.* to zero@localhost with grant option;
一起創建
grant all on db1.* to zero@localhost identified by'zero'
撤銷權限
revoke delete on db1.* from zero@localhost;
修改密碼
set password for zero@localhost = password('123');
刪除用戶
drop user zero@localhost
表關系
on update cascade # 設置級聯
on delete cascade不設置級聯只能先刪除依附表一對多的多的內容，多對多都不能刪除要先刪關系表
多對一
create table school (id int primary key,name char)
crsete table student(id int primary key, name char, nid int,foreign key (nid) references school(id));
一對一
create table husband(id int primary key, name char);
createtable wife (id int primary key, nid int unique,name char,foreign key(nid) references wife(id));
一對一注意外鍵對應字段設置唯一鍵
外鍵不為主鍵，必須為對方主鍵，數據類型要一致
多對多
create table student(id int primary key,name char );
create table lesson(id int primary key,name char(5));
create table xuanke(id int primary key, nid1 int,nid2 int,foreign key(nid1) references student(id),foreign key(nid2) references lesson(id))
關鍵是關系表建立
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