oracle 创建表和复制表，复制表结构，复制表数据 查询前N行

1.使用create table table_name_new as select * from table_name_old where 1=2;可以复制表结构
2.create table as 使用create table emp_copy as select * from scott.emp;可以复制表结构和数据
3.select (...) into (...) from table_name 复制数据时，在sqlserver中是可以的但是在oracle中提示缺失或错误，所以在复制数据的时候也可以用:insert into table1 (...) select (...) from table2 where (...)

4. 查询前n行

SELECT ROWNUM as RANK, ename, sal
FROM (SELECT ename,sal FROM emp_copy
ORDER BY sal DESC)
WHERE ROWNUM <= 10;

或者
SELECT e.empno,e.ename,e.sal FROM emp_copy e WHERE ROWNUM<=10
MINUS
SELECT e.empno,e.ename,e.sal FROM emp_copy e WHERE ROWNUM<=5;

或者

SELECT * FROM
(SELECT ROWNUM RN,e.empno,e.ename,e.sal FROM emp_copy e WHERE ROWNUM<=10) T
WHERE T.RN>5

/* 使用别名*/
select * from (
select rownum wn,e.ename "姓名",e.job "工作",e.sal "薪水",d.dname"部门名称" from emp_copy e,dept_copy d
where d.deptno=e.deptno
and d.deptno=20
and rownum<=4)t
where t.wn>=3

WN	姓名	工作	薪水	部门名称
3	SCOTT	ANALYST	3000.00	RESEARCH
4	ADAMS	CLERK	1100.00	RESEARCH