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create view empv20 as select empno,ename,job,hiredate,deptno from emp where deptno=20 with check option;
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create or replace view empv20 as select empno,ename,job,hiredate,deptno,sal from emp
where deptno=20 with check option;
Óï·¨£ºupdate ÊÓͼÃû set ¸üÐÂÄÚÈÝ Ìõ¼þ
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update empv20 set deptno=30 where empno=7369;
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update empv20 set ename='Ê·ÃÜ˹' where empno=7369;
´´½¨ÊÓͼʱÌí¼ÓÉÏwith read onlyÔò²»»á¶Ô´´½¨Ìõ¼þ¸üУ¬
create view empv20 as select empno,ename,job,hiredate,deptno from emp where deptno=20 with read only;
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update empv20 set deptno=30 where empno=7369;
update empv20 set ename='Ê·ÃÜ˹' where empno=7369;
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Óï·¨£ºcreate sequence ÐòÁÐÃû
·¶Àý£ºcreate sequence myseq
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Á½ÖÖ²Ù×÷£ºnextval—È¡µÃÐòÁеÄÏÂÒ»¸öÄÚÈÝ
          currval—È¡µÃÐòÁеĵ±Ç°ÄÚÈÝ
insert into ±íÃû(ÁÐÒ»£¬Áжþ) values(±íÃû.nextval,±íÃû.currval)£»
ɾ³ýÐòÁУºdrop sequence ÐòÁÐÃû
Ôö³¤·ù¶È£ºincrement by ³¤¶È£¨·ÅÔÚ´´½¨ÐòÁеĺó±ß£©
·¶Àý£º1£¬´´½¨ÐòÁÐcreate sequence myseq
      2£¬´´½¨±ícreate table testseq(next number,curr number);
      3£¬Öظ´²åÈëÊý¾Ýinsert into testseq(next,curr) values(myseq.nextval,myseq.currval);
      4£¬²éѯÊý¾Ýselect * from testseq;
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      Ó﷨Ϊ£ºcreate sequence ÐòÁÐÃû increment by n
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