SQL

Question

假设我有一个一对多的关系，想在某些 JOIN_ID 上连接两个表，但是对于每个不同的 JOIN_ID，我想限制结果中的行数至我该怎么做？

*甲骨文SQL

Answer 1

如果您的 RDBMS 支持 row_number()，那么您可以这样做：

select *
from (
  select 
      t1.*
    , t2.*
    , row_number() over (partition by t1.join_id order by t2.id) as rn
  from t1
    inner join t2
      on t1.join_id = t2.join_id
  ) as s
where rn < 6

Answer 2

我会这样做：

select t1.*, t2.*
from t1 join
     (select t2.*,
             row_number() over (partition by joinkey order by ??) as seqnum
      from t2
     ) t2
     on t1.joinkey = t2.joinkey and seqnum <= 6;

?? 用于指定顺序以定义要键入的行。例如，order by id desc 将保留具有最高 ID 的行。

SQL - 每场比赛最多加入 N 行

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greatest-n-per-group