在家懶得開Oracle, 用Postgresql代替.產生測試資料有些不同.
查詢部份也自己改成Oracle的函數就可以了.
create table g170610 (
  id serial primary key
, gname text not null
, gtype CHAR(1) not null
);

-- 產生 26 x 4 = 104 筆, 亂數排序
insert into g170610 (gname, gtype)
select n || m::text
     , chr(64+m)
  from (values ('趙'),('錢'),('孫'),('李')) a(n)
     , generate_series(1, 26) g(m)
 order by random();

select *
  from g170610;

 id  | gname | gtype 
-----+-------+-------
   1 | 趙3   | C
   2 | 錢19  | S
   3 | 李19  | S
...
 102 | 孫1   | A
 103 | 李1   | A
 104 | 孫21  | U
(104 筆資料列)
---------------------
with t1 as (
select gname
     , gtype
     , row_number() over (partition by gtype) as rn
  from g170610
)
select gname
     , gtype
  from t1
 where rn <= 2
 order by rn, gtype;

 gname | gtype 
-------+-------
 孫1   | A
 孫2   | B
 孫3   | C
 孫4   | D
 錢5   | E
 孫6   | F
 錢7   | G
 錢8   | H
 錢9   | I
 李10  | J
 孫11  | K
 孫12  | L
 錢13  | M
 錢14  | N
 李15  | O
 趙16  | P
 孫17  | Q
 錢18  | R
 李19  | S
 趙20  | T
 趙21  | U
 李22  | V
 李23  | W
 孫24  | X
 李25  | Y
 趙26  | Z
 李1   | A
 李2   | B
 趙3   | C
 趙4   | D
 趙5   | E
 李6   | F
 孫7   | G
 趙8   | H
 趙9   | I
 孫10  | J
 趙11  | K
 趙12  | L
 李13  | M
 孫14  | N
 錢15  | O
 孫16  | P
 趙17  | Q
 李18  | R
 趙19  | S
 孫20  | T
 李21  | U
 孫22  | V
 趙23  | W
 李24  | X
 趙25  | Y
 李26  | Z
(52 筆資料列)
 
----
要三組 就  rn <= 3

幸運叔祝大家幸運喔

CREATE TABLE tbldummy
(
 dname varchar2(4),
 dtype varchar2(1)
);

INSERT INTO tbldummy VALUES ('N001', 'A');
INSERT INTO tbldummy VALUES ('N002', 'B');
INSERT INTO tbldummy VALUES ('N003', 'C');
....
INSERT INTO tbldummy VALUES ('N026', 'Z');
INSERT INTO tbldummy VALUES ('N027', 'A');
INSERT INTO tbldummy VALUES ('N028', 'B');
INSERT INTO tbldummy VALUES ('N029', 'C');
....
INSERT INTO tbldummy VALUES ('N052', 'Z');
INSERT INTO tbldummy VALUES ('N053', 'A');
INSERT INTO tbldummy VALUES ('N054', 'B');
INSERT INTO tbldummy VALUES ('N055', 'C');
....
INSERT INTO tbldummy VALUES ('N078', 'Z');

(SELECT * FROM tbldummy WHERE dtype='A' AND ROWNUM < 3) UNION
(SELECT * FROM tbldummy WHERE dtype='B' AND ROWNUM < 3) UNION
(SELECT * FROM tbldummy WHERE dtype='C' AND ROWNUM < 3) UNION
....
(SELECT * FROM tbldummy WHERE dtype='Z' AND ROWNUM < 3);