mysql表操作-约束删除、用户填加、授权和撤权方式

show create table student3\G

alter table students3 drop primary key;

alter table student3 drop index student3_un_1;

alter table students drop check student3_chk_1;

alter table student3 drop check student3_chk_2;

alter table students modify stu_gender char(1);
alter table students drop check student3_chk_2;

alter table student3 drop constraint student3_fo_1;
alter table student3 drop key student3_fo_1;

show create table student3\G

show variables like '%validate_password%';

set global validate_password.lenggnt=3;

set global validate_password.policy=0;

create user testuser1@'%' identified by '123456',testuser2@'%' identified by '123456';

select host,user,authentication_string from mysql.user;

show grants for testuser1;

grant select,insert,update,create,alter,drop on mydb.* to testuser@'%';

show grants for testuser1;

show databases;

use mydb;

create table test(
-> id char(1),
-> name varchar(10)
-> );

revoke create,drop,alter on mydb.* from testuser1@'%';

show grants for testuser1;

show databases;

use mydb;

show tables;

create table test2(
-> id int,
-> name char(1)
-> );

grant all privileges on *.* to testuser2@'%';