最多2个基于其他列的常用值

Question

我有这张桌子：

Team | Player
Barca | Messi
Chelsea | Lampard
Barca | Messi
Barca | Messi
Chelsea | Lampard
Chelsea | Drogba
Barca | Iniesta
Barca | Xavi
Barca | Iniesta
Barca | Puyol

所以我需要一个查询来检索每个团队中前两位常见的玩家。像这样的东西：

Team | Player
Barca | Messi
Barca | Iniesta
Chelsea | Lampard
Chelsea | Drogba

Answer 1

您可以使用子查询/ CTE计算每个玩家的计数和排名，方法是按照每个团队的计数降序对行进行编号。然后从每个团队中拉出前两名球员：

查询（demo）：

with ranks as (
  select
    team, player, count(*) as count,
    row_number() over (partition by team order by count(*) desc) as teamrank
  from players p
  group by team, player
)
select
  team, player
from
  ranks
where teamrank <= 2
order by team, teamrank

<强>结果：

|    TEAM |  PLAYER |
---------------------
|   Barca |   Messi |
|   Barca | Iniesta |
| Chelsea | Lampard |
| Chelsea |  Drogba |

Answer 2

这是您想要窗口功能的地方：

select team, player
from (select team, player, count(*) as cnt,
             row_number() over (partition by team order by count(*) desc) as seqnum
      from team_player tp
      group by team, player
     ) tp
where seqnum in (1, 2)

请注意，这会在Windows函数中嵌套聚合函数count(*)。