Sql 限制记录分组

Question

我有一个table'Players' 在此 table 中，列是 'ID','surname','nation' 我需要一个查询，结果必须显示按国家/地区限制为 4 个国家/地区的玩家列表前任 Table 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

具有row_number()window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

参见demo。
或者，如果您的 SQLite 版本不支持 window 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

参见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 |

Sql 限制记录分组

Sql limit record grouped

sql

sqlite

group-by

limit