新建表：
1 -- Create table 2 create table EMP 3 ( 4 empno NUMBER(4), 5 ename VARCHAR2(10), 6 job VARCHAR2(9), 7 mgr NUMBER(4), 8 hiredate DATE, 9 sal NUMBER(7,2), 10 comm NUMBER(7,2), 11 deptno NUMBER(2) 12 ) 13 tablespace USERS 14 pctfree 10 15 initrans 1 16 maxtrans 255 17 storage 18 ( 19 initial 64K 20 next 1M 21 minextents 1 22 maxextents unlimited 23 ); 24 -- Add comments to the columns 25 comment on column EMP.empno 26 is ‘编码‘; 27 comment on column EMP.ename 28 is ‘名称‘; 29 comment on column EMP.job 30 is ‘工作‘; 31 comment on column EMP.mgr 32 is ‘主管‘; 33 comment on column EMP.hiredate 34 is ‘聘用时间‘; 35 comment on column EMP.sal 36 is ‘工资‘; 37 comment on column EMP.comm 38 is ‘提成‘; 39 comment on column EMP.deptno 40 is ‘部门编码‘;
初始化数据：
1 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 2 values (7369, ‘SMITH‘, ‘CLERK‘, 7902, to_date(‘27-12-1980‘, ‘dd-mm-yyyy‘), 800.00, null, 20, 7369, ‘SMITH‘); 3 4 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 5 values (7499, ‘ALLEN‘, ‘SALESMAN‘, 7698, to_date(‘20-02-1981‘, ‘dd-mm-yyyy‘), 1600.00, 300.00, 30, 7499, ‘SALESMAN‘); 6 7 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 8 values (7521, ‘WARD‘, ‘SALESMAN‘, 7698, to_date(‘22-02-1981‘, ‘dd-mm-yyyy‘), 1250.00, 500.00, 30, 7521, ‘WARD‘); 9 10 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 11 values (7566, ‘JONES‘, ‘MANAGER‘, 7839, to_date(‘02-04-1981‘, ‘dd-mm-yyyy‘), 2975.00, null, 20, 7566, ‘MANAGER‘); 12 13 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 14 values (7654, ‘MARTIN‘, ‘SALESMAN‘, 7698, to_date(‘28-09-1981‘, ‘dd-mm-yyyy‘), 1250.00, 1400.00, 30, 7654, ‘SALESMAN‘); 15 16 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 17 values (7698, ‘BLAKE‘, ‘MANAGER‘, 7839, to_date(‘01-05-1981‘, ‘dd-mm-yyyy‘), 2850.00, null, 30, 7698, ‘MANAGER‘); 18 19 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 20 values (7782, ‘CLARK‘, ‘MANAGER‘, 7839, to_date(‘09-06-1981‘, ‘dd-mm-yyyy‘), 2450.00, null, 10, 7782, ‘MANAGER‘); 21 22 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 23 values (7788, ‘SCOTT‘, ‘ANALYST‘, 7566, to_date(‘19-04-1987‘, ‘dd-mm-yyyy‘), 3000.00, null, 20, 7788, ‘SCOTT‘); 24 25 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 26 values (7839, ‘KING‘, ‘PERSIDENT‘, null, to_date(‘17-11-1981‘, ‘dd-mm-yyyy‘), 5000.00, null, 10, 7839, ‘PERSIDENT‘); 27 28 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 29 values (7844, ‘TURNER‘, ‘SALESMAN‘, 7698, to_date(‘28-09-1981‘, ‘dd-mm-yyyy‘), 1500.00, 0.00, 30, 7844, ‘TURNER‘); 30 31 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 32 values (7876, ‘ADAMS‘, ‘CLERK‘, 7788, to_date(‘23-05-1987‘, ‘dd-mm-yyyy‘), 1100.00, null, 20, 7876, ‘CLERK‘); 33 34 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 35 values (7900, ‘JAMES‘, ‘CLERK‘, 6798, to_date(‘03-12-1981‘, ‘dd-mm-yyyy‘), 950.00, null, 30, 7900, ‘JAMES‘); 36 37 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 38 values (7902, ‘FORD‘, ‘ANALYST‘, 7566, to_date(‘03-12-1981‘, ‘dd-mm-yyyy‘), 3000.00, null, 20, 7902, ‘FORD‘); 39 40 insert into emp (EMPNO, ENAME, JOB, MGR, HIREDATE, SAL, COMM, DEPTNO, GREATEST(T.SAL,T.EMPNO), GREATEST(T.ENAME,T.JOB)) 41 values (7934, ‘MILLER‘, ‘CLERK‘, 7782, to_date(‘23-01-1982‘, ‘dd-mm-yyyy‘), 1300.00, null, 10, 7934, ‘MILLER‘);
示例一：
1 select t.empno, t.sal, comm, nvl(t.comm, -1) from emp t order by 4;
结果：
示例二：
1 select t.empno, t.sal, comm, nvl(t.comm, -1) from emp t order by 3 nulls first
结果：
结论：
order by nulls first 表示空值在前
order by nulls last 表示空值在后
原文地址：https://www.cnblogs.com/sxyu2018/p/9895374.html
时间： 2024-08-02 08:25:27