????????????
??????1?????????
????create user //????????dba???????????
????create user scott(?????)  identified by tiger??????;
??????2????????
????drop  user  ???????
????????????????????????dba???????????????
??????3???????????????????????????????????????????cascade????????????????????????
??????4???′????????????κ?????system??sys??????丳????
???????????????????system?????
????grant connect to scott;    (connect???) //??????
????grant  resource to scott;   //???????
???????????????
????(?????????sys??system)  grant  select  on emp????? to  scott;  ??emp??????????scott
????scott??????select  *  from  owner.emp
????(????)

????????????select??insert ??update??delete??all??create index....????????
?????????   resource?????κ???????佨??
????connect
????dba:??????????????dba
???????????revoke  (????????????)
????revoke select?????????? on emp????? from scott;