在SQL Server里面有top关键字可以很方便的取出前N条记录，但是Oracle里面却没有top的使用，类似实现取出前N条记录的简单方法如下：
方法1：利用ROW_NUMBER函数
取出前5条记录：
SELECT NO FROM (
SELECT ROW_NUMBER() OVER (ORDER BY NO) RNO, NO FROM ROWNUM_TEST
)WHERE RNO <= 5 ORDER BY NO ;
|
取出中间5条记录：
|
1
2
3
|
SELECT NO FROM (
SELECT ROW_NUMBER() OVER (ORDER BY NO) RNO, NO FROM ROWNUM_TEST
) WHERE RNO BETWEEN 5 AND 10 ORDER BY NO;
|
方法2：利用子查询
取出前5条记录：
|
1
2
3
|
SELECT NO FROM (
SELECT NO FROM ROWNUM_TEST ORDER BY NO
)WHERE ROWNUM <= 5 ORDER BY NO ;
|
取出中间5条记录：
|
1
2
3
4
5
|
SELECT NO FROM (
SELECT NO, ROWNUM RNO FROM (
SELECT NO FROM ROWNUM_TEST ORDER BY NO
)
) WHERE RNO BETWEEN 5 AND 10 ORDER BY NO;
|
选出累计访问量最大的10个ip地址，并按访问量降序排列。
select top 10 ip, countip from
(select ip,count(*) as countip from records group by ip) a
order by countip desc