一、事物例子说明

create table student(
    uuid char(32) default sys_guid() not null primary key,name varchar(32)
);

insert into system.student (name) values ('huangbiao');
insert into system.student (name) values ('liumei');

备注：sys_guid()函数产生的数据只有32位。

sql> select * from student;

UUID NAME

------------------------------------ ------------

00D4A520B3EE46CC85333591A072031C huangbiao

5C2634E72D5A405BA6342B1673178818 liumei

savepoint a1;

delete from student where name='huangbiao';

select * frsql> savepoint a1;

Savepoint created.

sql> delete from student where name='huangbiao';

1 row deleted.

sql> select * from student;

UUID NAME

------------------------------------ -----------

5C2634E72D5A405BA6342B1673178818 liumeiom emp;

sql> savepoint a2;

Savepoint created.

sql> delete from student where name='liumei';

1 row deleted.

sql> select * from student;

no rows selected

sql> rollback to a2;

Rollback complete.

sql> select * from student;

UUID NAME

------------------------------------ -------

5C2634E72D5A405BA6342B1673178818 liumei

sql> rollback to a1;

Rollback complete.

sql> select * from student;

UUID NAME

------------------------------------ ------------

00D4A520B3EE46CC85333591A072031C huangbiao

5C2634E72D5A405BA6342B1673178818 liumei

备注：这里不能使用commit命令，否则之前所用的savepoint都将全部不起作用了。

二、只读事务

只允许执行查询操作，不允许其它的DML操作事务，使用只读事务可以确保用户只能读取某时间点的数据，之后的数据将不会理睬。

例如机票代售点每天18点开始统计今天的销售情况，但是18点肯定还有人在操作数据库，因此这里使用只读事务之后就不会对统计造成影响。

1、打开PLsql(1)工具输入：

set transaction read only;

sql> select * from student;

UUID NAME

-------------------------------- ---------

E622460F590C43C8BF746A3F43622DE3 huangbiao

40C039E5536E45A9905383333B05E499 liumei

2、打开另一个PLsql(2)工具

insert into system.student (name) values ('zhangsan');

3、使用PLsql(1)查询数据

sql> select * from student;

UUID NAME

-------------------------------- ---------

E622460F590C43C8BF746A3F43622DE3 huangbiao

40C039E5536E45A9905383333B05E499 liumei

结果：发现第一个查询的数量和第二个PLSQL查询的数量是不一致的，这就是设置只读事务的功能

设置只读事务之后，将不会显示当前时间点之后的所有操作数据

4、使用PLsql(1)插入数据

sql> insert into system.student (name) values ('lisi');

insert into system.student (name) values ('lisi')

*

ERROR at line 1:

ORA-01456: may not perform insert/delete/update operation inside a READ ONLY

transaction

三、java代码设置手动提交

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.sqlException;
import java.sql.Statement;

public class TestTrans {

	public static void main(String[] args) {
		Connection conn = null;
		Statement stmt = null;
		try {
			DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
			System.out.println("driver is ok");
			conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl","system","admin");
			//不让oracle自动提交，而是手动提交数据
			conn.setAutoCommit(false);
			System.out.println("connection is ok");
			stmt = conn.createStatement();
			String sql1 = "update scott.emp set sal=sal-100 where ename='SMITH'";
			String sql2 = "update scott.emp set sal=sal-100 where ename='SCOTT'";
			stmt.execute(sql1);
			//这段代码是模拟操作出现异常的方法
			int a = 1/0;
			stmt.execute(sql2);
			//执行完上面两个sql语句之后才commit
			conn.commit();
		} catch (sqlException e) {
			try {
			//如果出现异常将操作回滚，这样就能保证数据的一致性
				conn.rollback();
			} catch (sqlException e1) {
				// TODO Auto-generated catch block
				e1.printStackTrace();
			}
			e.printStackTrace();
		}
		
		if(stmt!=null){
			try {
				stmt.close();
			} catch (sqlException e) {
				e.printStackTrace();
			}
		}
		if(conn!=null){
			try {
				conn.close();
			} catch (sqlException e) {
				e.printStackTrace();
			}
		}
	}
}