1，行转列函数:
复制代码 代码示例:
select wm_concat(username) from users
2，查询重复记录函数
复制代码 代码示例:
select t.* from(select t.*,rownum rn from USERS t where t.username in (select username from USERS group by username having count(*) > 1)) t
3，过滤表中重复记录函数
有一张User表，姓名字段重复
A：
复制代码 代码示例:
select t.* from(select t.*,rownum rn from USERS t where t.username not in (select username from USERS group by username having count(*) > 1))t
union all
select t.* from(select t.*,rownum rn from USERS t where t.username in (select username from USERS group by username having count(*) > 1)) t where t.rn=1
B：
复制代码 代码示例:
select * from (select t. *,row_number() over(partition by username order by username) rn from USERS t) tt where tt.rn=1;
其它用法，可以研究下oracle中的exists 和not exists语句。
