急 ！Oracle 列查询问题

[EM265]

//希望各位帮帮忙啊！衷心感谢
		/**
		 * 数据库为: Oracle10g
		 * 现在有一张表名为student的表，数据如下：
		 * ID	NAME	AGE
		 * 1	A		20
		 * 2	B		20
		 * 3	C		20	
		 * 4	X		19
		 * 5	Y		19
		 */
		
		/**
		 * 期望结果(一)
		 * 下面我想通过一条sql语句或者储存过程 查询AGE=20的相关记录
		 * 查询结果需要如下：(只查询ID、NAME列就可以了)
		 * ID			NAME		
		 * 1,2,3        A,B,C		
		 */
		
		/**
		 * 期望结果(二)
		 * 最好是能查询出这样的结果(根据AGE来查，我想的话应该会用Group By吧)
		 * ID			NAME		
		 * 1,2,3        A,B,C	
		 * 4,5			X,Y
		 * 
		 */

[wangyong174013]

select wm_concat(id) "ID",wm_concat(name) "name" from student
group by age;

[oraclemch]

create table student
(
       id number,
       name varchar2(20),
       age number
);

insert into student
select 1 ,   'A'   ,    20 from dual
union select        2 ,   'B',       20 from dual
union select        3,    'C' ,       20 from dual 
union select        4,    'X',       19 from dual
union select        5,    'Y' ,      19 from dual;

1,期望结果(一)
select wm_concat(id) as ID ,wm_concat(name) as NAME from student 
group by age having age=20;
--结果如下：
  ID      NAME
	1,2,3	  A,C,B


2,期望结果(二)
select wm_concat(id) as ID ,wm_concat(name) as NAME from student 
group by age order by age desc;
--结果如下：
  ID      NAME
  1,2,3	  A,C,B
  4,5	    X,Y  

[小灰狼W]

1.
select wm_concat(id)id,wm_concat(name)name
from student where age=20
2.
select wm_concat(id)id,wm_concat(name)name
from student
group by age