Question

我有一个相当困难的查询。我需要在名为＆＃39; key_phrases＆＃39;的表上写一个查询。（列：＆＃39;用户＆＃39;，＆＃39;词组＆＃39; tfw＆＃39;），它检索每个用户的前10％行，其中列的值最高＆＃ 39; TFW＆＃39 ;.该查询应返回所有列。提前谢谢，Nil

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

使用应该更快的变量的另一个查询

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

SQL选择前n％行

1 个答案: