conn system/manager--创建实验用户grant connect,resource to test identified by test;conn test/test--创建实验表1create table a(a number);insert into a values(1);commit;select * from a for update;或select * from a for update of a.a;（a表的a列）--新打开一个SQL*Plus窗口conn test/test（test用户上的第二个会话）delete from a;