oracle防止丢失更新[乐观锁ora_rowscn]

--[b]默认ora_rowscn记录block上更改[/b] 创建表时添加关键字rowdependencies就能记录行上更改--添加rowdependencies后每行增加6字节长度--建表语句create table EMP_scn(  empno    NUMBER(4) not null,  ename    VARCHAR2(10),  job      VARCHAR2(9),  mgr      NUMBER(4),  hiredate DATE,  sal      NUMBER(7,2),  comm     NUMBER(7,2),  deptno   NUMBER(2))rowdependencies;--查询语句 select t.*,rowid,scn_to_timestamp(ora_rowscn), ora_rowscn from emp_scn t;--更新时能用ora_rowscn来判断改行数据是否已经被更新