無法順序結果時正確分組

Question

CREATE TABLE test(
id integer, 
content text, 
number integer 
) 

INSERT INTO test(id,content,number) VALUES(1,'a'::text, 5); 
INSERT INTO test(id,content,number) VALUES(2,'b'::text, 2); 
INSERT INTO test(id,content,number) VALUES(3,'c'::text, 2); 
INSERT INTO test(id,content,number) VALUES(4,'d'::text, 3); 
INSERT INTO test(id,content,number) VALUES(5,'e'::text, 1); 
INSERT INTO test(id,content,number) VALUES(6,'f'::text, 3); 
INSERT INTO test(id,content,number) VALUES(7,'g'::text, 3); 
INSERT INTO test(id,content,number) VALUES(8,'h'::text, 2); 
INSERT INTO test(id,content,number) VALUES(9,'i'::text, 4); 

我想要的是，將數字列和排序結果分組爲id列作爲desc，像這樣;

| id | number 
---------------- 
| 9 | 4 
| 8 | 2 
| 7 | 3 
| 5 | 1 

這裏有多個外觀像2,​​3和1的所有號碼進行分組，看到只有一次，還下令用id柱遞減。

我試過這個查詢，但它不適合我;

SELECT DISTINCT ON (number) number, id FROM test ORDER BY number,id DESC LIMIT 4 

Answer 1

使用派生表：

SELECT id, number 
FROM (
    SELECT DISTINCT ON (number) number, id 
    FROM test 
    ORDER BY number, id DESC 
    ) s 
ORDER BY id DESC 
LIMIT 4; 

id | number 
----+-------- 
    9 |  4 
    8 |  2 
    7 |  3 
    5 |  1 
(4 rows) 

Answer 2

你還可以：

select max(id) as id, number 
from test 
group by number 
order by id desc 
limit 4