oracle explain plan

explain plan的两种方式：

 

一、SQL方式：

explain plan for select count(*) from emp;

select * from table(dbms_xplan.display);

 

 

二、AUTOTRACE方式：

开启set autotrace on 后，提示：

Unable to gather statistics please unsure user has correct access.
The statistic feature requires that the user is granted select on v_$sesstat, v_$statname and v_$session.

 按要求对三个视图grant select后，还是报错，还需对v_$mystat也grant select