mysql - SQL 选择前 n% 行

Question

我有一个相当困难的问题。我需要在名为“key_phrases”(列:“user”、“phrase”、“tfw”)的表上编写一个查询，该表检索每个用户的前 10% 行，这些行具有列“tfw”的最高值。查询应返回所有列。提前致谢，无

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

另一个使用变量的查询应该更快

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