如何通过在特定列中使用不同的值来执行结果限制？

Question

鉴于我有这个数据集。

Player         Team         Date_Played
John Smith     New York     2/25/2014
Joe Smith      New York     2/25/2014
Steve Johnson  New York     2/25/2014
Steph Curry    Orlando      2/25/2014
Frank Anthony  Orlando      2/26/2014
Brian Smith    Bulls        2/26/2014
Steve Johnson  Bulls        2/27/2014
Steph Curry    Bulls        2/28/2014
Ben Smith      Bulls        3/28/2014

我想知道如何编写一个返回每个团队玩家数量一半的查询。我希望它看起来像这样：

Player         Team         Date_Played
John Smith     New York     2/25/2014
Joe Smith      New York     2/25/2014
Steph Curry    Orlando      2/25/2014
Brian Smith    Bulls        2/26/2014
Steve Johnson  Bulls        2/27/2014

我考虑过尝试使用LIMIT或TOP命令，但我不知道如何根据特定列中的不同值编写查询来限制结果。 有任何想法吗？这可能吗？

Answer 1

您可以使用窗口功能。我会使用row_number()和count()：

select t.*
from (select t.*, count(*) over (partition by team) as cnt,
             row_number() over (partition by team order by team) as seqnum
      from t
     ) t
where seqnum <= 0.5 * cnt;

还有其他使用单一功能的方法，例如ntile()：

select t.*
from (select t.*, 
             ntile(2) over (partition by team order by team) as tile
      from t
     ) t
where tile = 1;

或percentile()或其他人。