说明：
floor函数：向下取整，比如floor(2.5) = 2;floor(3.0) = 3;
查询：
select floor(e2.r/ 2),floor((e2.r-1)/2)，e2.* from
(select rownum r, e1.* from
(
select * from nhlh_sto_yggys_mid where f_pkey in (select f_pkey from nhlh_sto_yggys_mid group by f_pkey having count(1) >1) order by f_pkey
) e1
) e2 where floor(e2.r/ 2) >floor((e2.r-1)/2) ;
结果：
解释：因为表中没有行数列，所以首先我们查询加入行数
select rownum r, e1.* from
(
select * from nhlh_sto_yggys_mid where f_pkey in (select f_pkey from nhlh_sto_yggys_mid group by f_pkey having count(1) >1) order by f_pkey
) e1
然后我们通过取整函数判断行数除2与行数减1除2的结果对比，从而查询出所需结果。查询奇数行也是一样的道理。