drop：刪除屬性或約束，常見格式
add：添加屬性或約束
modify：修改屬性類型及約束
change：重命名屬性修改類型及約束
constraint：手動指定約束名

create database test; use test; create table Students( S_ID integer, S_NAME varchar(10) not null, S_AGE integer, S_TEL varchar(11) null, primary key(S_ID)); insert into Students values(1,'TOM',14,'13223616367'); #插入元組 insert into Students values(2,'JACK',14,'13245277581'); #插入元組 select * from Students; #Students表展示#刪除S_TEL屬性 alter table Students drop column S_TEL; select * from Students;#添加S_TEL屬性 alter table Students add column S_TEL varchar(11); select * from Students;#修改S_TEL類型以及約束 alter table Students modify column S_TEL varchar(15); select * from Students;#屬性重命名，修改類型以及約束 alter table Students change column S_TEL S_phonenum varchar(11); select * from Students;#表重命名 alter table Students rename to Stu; select * from Stu;#刪除主鍵 alter table Stu drop primary key; select * from Stu;#添加主鍵 alter table Stu add primary key(S_ID); select * from Stu;#添加唯一性約束 alter table Stu add constraint cons_0 unique index (S_phonenum); select * from Stu;#刪除唯一性約束 alter table Stu drop index cons_0; select * from Stu;

總結

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