如何获取数据库表中前 x% 的值

Question

如何获取数据库表中前 x% 的值。

例如，我有一个日志文件，我将它加载到一个 db 表中。我想丢弃运行时间最长的 1% 的请求，因为它们会扭曲数据。

有什么简单的方法吗？

顺便说一句，我正在使用 derby 数据库。

谢谢

Answer 1

您需要累积百分比还是个人百分比？我不知道使用 Derby 计算累积总数的方法，但我知道 H2 数据库/MySQL 的方法。所以只有我的示例的第一部分适用于 Derby。对于 MySQL，您需要将 CAST(... AS INTEGER) 替换为 CAST(... AS SIGNED INTEGER)：

drop table test;
create table test(data int);
create index idx_test_data on test(data desc);
insert into test values(1), (1), (1), (2);
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test select data from test;
insert into test values(100), (200), (800);
select sum(data), count(*) from test;

select data, (data * 100. / (select sum(data) from test)) percent
from test where data * 100. / (select sum(data) from test) < 1 order by data desc;

select @acc := 0, @total := sum(data) from test;
create table pa as select data, cast(@acc := @acc + (data * 100. / @total) as integer) percent_acc
from test order by data desc;
select * from pa where percent_acc > 2 limit 10;
drop table pa;