急sql 优化 下面sql要优化吗,该如何处理

急！！！！sql 优化 下面sql要优化吗
如何优化如下sql

SQL code

/*1.1*/select e.ename,e.hiredate from emp ewhere e.hiredate=(select min(hiredate) from emp) or  e.hiredate=(select max(hiredate) from emp);/*1.2*/select grade,count(*)from emp e,salgrade swhere sal<=s.hisal and sal>=s.losalgroup by grade;/*1.3*/select d.dname,sum(e.sal)from emp e,dept dwhere d.deptno=e.deptnogroup by d.dname;/*1.4*/select e.deptno,e.ename,e.salfrom emp eorder by e.deptno,e.sal desc;/*1.5*/select e1.ename,e2.ename manger from emp e1,(select empno,ename from emp) e2 where e1.mgr=e2.empno/*1.6*/select e.deptno,sum(e.sal+nvl(e.comm,0)),avg(e.sal+nvl(e.comm,0)),max(e.sal+nvl(e.comm,0)),min(e.sal+nvl(e.comm,0))from emp egroup by e.deptno;