今天学习事务控制
默认方式启动事务：
开启一个事务，设置事务的隔离级别为READ COMMITTED，访问模式为READ ONLY
以隔离级别为repeatable read，读/写方式启动事务
没有建成功：
savepoint测试：
这个好奇怪。因为前面有个insert语句打错了，结果连后面的insert都无法执行？
重来一遍：
开始做作业：
1.以默认方式启动事务1，修改事务隔离级别，查看transaction_isolation
start transaction;
show transaction_isolation;
现在隔离级别为 读提交。
修改成别的：可重复读。
START TRANSACTION ISOLATION LEVEL repeatable read READ WRITE;
2.以读写方式启动事务2，创建新表，修改事务为只读事务，查看transaction_read_only，并向表中插入记录
create table table2(a int);
SET LOCAL TRANSACTION ISOLATION LEVEL READ COMMITTED READ ONLY;
show transaction_read_only;
insert into table2 value(9);
rollback;
3.启动事务3，对表进行增删改查，并用到创建savepoint，回滚savepoint和删除savepoint
create table table2(id int);
begin transaction;
insert into table2 values(1);
insert into table2 values(2);
savepoint my_poi;
select * from table2;
insert into table2 values(3);
insert into table2 values(4);
delete from table2 where id=2;
select * from table2;
savepoint my_poi2;
select * from table2;
rollback to savepoint my_poi2;
select * from table2;
insert into table2 values(5);
select * from table2;
rollback to savepoint my_poi2;
select * from table2;
release savepoint my_poi2;
rollback to savepoint my_poi;
select * from table2;
release savepoint my_poi;
4.清理数据
drop table table2;
commit;
