create database two20210611 default charset=utf8;
use two20210611;
create table student (
studentid char(10) PRIMARY key,
studentname varchar(10) not null,
gender varchar(2) ,
age int ,
index(studentname)
);
show create table student;
insert into student values ('1' , '丘处机' , '男' , 46 );
select * from student;
-- 执行计划 explain
explain select * from student where studentname="丘处机";
-- 组合索引
create table student2 (
studentid char(10) PRIMARY key,
studentname varchar(10) not null,
age int ,
city varchar(10),
dormitoryNo varchar(5), # 宿舍编号
index MultiIndex(city,dormitoryNo) # 组合索引
);
show create table student2;
insert into student2 values ('1' , '杨过' , 19 , '活死人墓' , '002') ;
select * from student2 where studentname="杨过";
explain select * from student2 where studentname="杨过";
select * from student2 where city="活死人墓" and dormitoryNo ='002';
explain select * from student2 where city="活死人墓" and dormitoryNo ='002';
-- 删除索引
alter table student drop index studentname;
-- 创建索引
create index studentname on student(studentname) ;
-- 事务
create table user(
u_name varchar(20) ,
unique(u_name)
);
insert into user values ("小龙女");
select * from user;
begin;
insert into user values ("李莫愁");
commit;
begin; -- 事务的开始
insert into user values ("尹志平");
commit; -- 事务的结束
begin ;
insert into user values ("郭靖");
rollback; -- 回滚
-- 回滚点
begin;
insert into user values ("A");
savepoint first_point;
insert into user values ("B");
rollback to savepoint first_point;
insert into user values("C");
commit;
select * from user ;
