Oracle之PL/SQL有关查询实现

最近有看到网上关于排序查询的实现有两个自己不常用的查询语法，关于分析函数的用法，记之，鉴之，勉之；

在一个表里怎么查询每列数据的最大值和次大值？

WITH tt
        AS (SELECT CASE WHEN col1 IN (1, 2) THEN empno ELSE NULL END empno,
                   CASE WHEN col2 IN (1, 2) THEN ename ELSE NULL END ename,
                   CASE WHEN col3 IN (1, 2) THEN job ELSE NULL END job,
                   CASE WHEN col4 IN (1, 2) THEN mgr ELSE NULL END mgr,
                   CASE WHEN col5 IN (1, 2) THEN hiredate ELSE NULL END
                      hiredate,
                   CASE WHEN col6 IN (1, 2) THEN sal ELSE NULL END sal,
                   CASE WHEN col7 IN (1, 2) THEN comm ELSE NULL END comm,
                   CASE WHEN col8 IN (1, 2) THEN deptno ELSE NULL END deptno
              FROM (SELECT empno,
                           ROW_NUMBER () OVER (ORDER BY empno DESC) col1,
                           ename,
                           ROW_NUMBER () OVER (ORDER BY ename DESC) col2,
                           job,
                           ROW_NUMBER () OVER (ORDER BY job DESC) col3,
                           mgr,
                           ROW_NUMBER () OVER (ORDER BY mgr DESC) col4,
                           hiredate,
                           ROW_NUMBER () OVER (ORDER BY hiredate DESC) col5,
                           sal,
                           ROW_NUMBER () OVER (ORDER BY sal DESC) col6,
                           comm,
                           ROW_NUMBER () OVER (ORDER BY comm DESC) col7,
                           deptno,
                           ROW_NUMBER () OVER (ORDER BY deptno DESC) col8
                      FROM emp))
SELECT MAX (empno) empno,
       MAX (ename) ename,
       MAX (job) job,
       MAX (mgr) mgr,
       MAX (hiredate) hiredate,
       MAX (sal) sal,
       MAX (comm) comm,
       MAX (deptno) deptno
  FROM tt
UNION ALL
SELECT MIN (empno) empno,
       MIN (ename) ename,
       MIN (job) job,
       MIN (mgr) mgr,
       MIN (hiredate) hiredate,
       MIN (sal) sal,
       MIN (comm) comm,
       MIN (deptno) deptno
  FROM tt

对一张表中的数据做如下操作啊，先对数据进行分分组，再在组内进行排序，再显示每组中的前两行

select * from (select d.empno,
       d.deptno,
       sum(sal),
       rank() over(partition by deptno order by sum(sal) desc) rank
  from scott.emp d
 group by d.empno, d.deptno) where rank<3