SQL Select Top n percent rows

Question

我有一個相當困難的查詢。 我需要在一個名爲'key_phrases'（列：'user'，'phrase'，'tfw'）的表上寫一個查詢，它爲每個用戶檢索前10％的行，列'tfw' 。查詢應該返回所有列。 由於事先無

Answer 1

select user, phrase, tfw 
from key_phrases t1 
join (
    select count(*) total_rows_per_user, user 
    from key_phrases 
    group by user 
) t2 on t1.user = t2.user 
where (
    select count(*) from key_phrases t3 
    where t3.user = t1.user 
    and t3.tfw >= t1.tfw 
)/total_rows_per_user <= .1 

使用變量另一個查詢應該是更快

select user, phrase, tfw, 
if(@prev_user = user, @user_count := @user_count + 1, @user_count := 1), 
@prev_user := user 
from key_phrases t1 
join (
    select count(*) total_rows_per_user, user 
    from key_phrases 
    group by user 
) t2 on t1.user = t2.user 
cross join (select @user_count := 1, @prev_user := null) t3 
where @user_count/total_rows_per_user >= .9 
order by user, tfw