In order to execute a SQL statement, internally oracle issues n number of SQL statements on the data dictionary which are called recursive SQL statements. We are least bothered about the performance of recursive SQL statements, that is the reason "sys=no".
Note : Whenever possible, use bind variables rather than literals.
scott>select * from emp where empno=1278;
scott>select * from EMP where empno=1278;
scott>select * from emp where empno=:a;
a!=A
