sql系列（基础篇）-第二章约束和排序数据(五)
81-09-28 1250 1400 30
7521 WARD SALESMAN 7698 1981-02-22 1250 500 30
7499 ALLEN SALESMAN 7698 1981-02-20 1600 300 30
7844 TURNER SALESMAN 7698 1981-09-08 1500 0 30
14 rows selected.
注意：null 值之间的排序不考虑（因为Null 和 null 之间无法比较大小）
如果我想将comm有值的部分换到上面，该怎么办？
SCOTT@ORCL>select * from emp
2 order by comm desc nulls last;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- ---------- ---------- ---------- ----------
7654 MARTIN SALESMAN 7698 1981-09-28 1250 1400 30
7521 WARD SALESMAN 7698 1981-02-22 1250 500 30
7499 ALLEN SALESMAN 7698 1981-02-20 1600 300 30
7844 TURNER SALESMAN 7698 1981-09-08 1500 0 30
7788 SCOTT ANALYST 7566 1987-04-19 3000 20
7839 KING PRESIDENT 1981-11-17 5000 10
7876 ADAMS CLERK 7788 1987-05-23 1100 20
7900 JAMES CLERK 7698 1981-12-03 950 30
7902 FORD ANALYST 7566 1981-12-03 3000 20
7934 MILLER CLERK 7782 1982-01-23 1300 10
7698 BLAKE MANAGER 7839 1981-05-01 2850 30
7566 JONES MANAGER 7839 1981-04-02 2975 20
7369 SMITH CLERK 7902 1980-12-17 800 20
7782 CLARK MANAGER 7839 1981-06-09 2450 10
14 rows selected.
同理：自己验证 升序 排列
SCOTT@ORCL>
select * from emp
2 order by comm asc nulls first;