sql限制记录分组

Question

我有一张“玩家”表 在此表中，列是'ID','surname','nation' 我需要一个查询，结果必须显示一个由国家限制为 4 个国家的玩家列表 前任 桌面玩家

ID   surn.. nation
1    Garcia   spa
2    smith    gbr
3    rossi    ita
4    villa    spa
5    renoir   fra
6    muller   ger
7    conti    ita
8    johnson  usa
9    james    gbr
10   lopez    spa
11   dubois   fra
12   petit    fra
13   popov    rus
14  rodriguez spa
15   weber    ger
16   ivanov   rus
17  gonzales  spa
18   wagner   ger
19   bruni    ita
20   Smirnov  rus
21   white    gbr
22   schmidt  ger
23  Armstrong usa
24    green   gbr
25   Schulz   ger 

结果集

Nation| surname-
Spa |Garcia-
Spa| villa-
Spa| lopez-
Spa |rodriguez-
Gbr |smith-
Gbr |james-
Gbr| white-
Gbr| green -
Ita| rossi-
Ita |conti-
Ita |bruni-
Fra |renoir-
Fra| dubois-
Fra| petit-
Ger |muller-
Ger| weber-
Ger| wagner-
Ger |schmidt-
Usa |johnson -
Usa |armstrong-
Rus| popov-
Rus |ivanov-
Rus |Smirnov -

Answer 1

带有row_number()窗口功能：

select t.nation, t.surname
from (
  select *,
    row_number() over (partition by nation order by id) rn
  from players
) t
where t.rn <= 4
order by t.nation, t.id

请参阅demo。
或者如果您的 SQLite 版本不支持窗口函数：

select t.nation, t.surname
from (
  select p.*,
    (select count(*) + 1 from players where nation = p.nation and id < p.id) rn
  from players p
) t
where t.rn <= 4
order by t.nation, t.id

请参阅demo。
结果：

| nation | surname   |
| ------ | --------- |
| fra    | renoir    |
| fra    | dubois    |
| fra    | petit     |
| gbr    | smith     |
| gbr    | james     |
| gbr    | white     |
| gbr    | green     |
| ger    | muller    |
| ger    | weber     |
| ger    | wagner    |
| ger    | schmidt   |
| ita    | rossi     |
| ita    | conti     |
| ita    | bruni     |
| rus    | popov     |
| rus    | ivanov    |
| rus    | Smirnov   |
| spa    | Garcia    |
| spa    | villa     |
| spa    | lopez     |
| spa    | rodriguez |
| usa    | johnson   |
| usa    | Armstrong |