SQL：快速累积频率查询（postgres）

Question

我期待从我们的数据库中获取累积频率数据。我创建了一个简单的临时表，其中包含我们所见过的所有唯一状态更新计数以及具有这些状态更新量的用户数。

 Table "pg_temp_4.statuses_count_tmp" 
    Column  | Type | Modifiers 
----------------+---------+----------- 
statuses_count | integer | 
frequency  | bigint | 
Indexes: 
    "statuses_count_idx" UNIQUE, btree (statuses_count) 

我当前的查询是：

select statuses_count, frequency/(select * from total_statuses)::float, (select sum(frequency)/(select * from total_statuses)::float AS percentage from statuses_count_tmp WHERE statuses_count <= SCT.statuses_count) AS cumulative_percent FROM statuses_count_tmp AS SCT ORDER BY statuses_count DESC; 

但这需要相当长一段时间，查询的数量相当迅速增长。因此，对于我拥有的50,000行，我正在查看50k阶乘行数来读取。坐在这里看着这个疑问，我希望这是一个更好的解决方案，但我还没有完成。

希望能得到这样的：

0  0.26975161  0.26975161 
1  0.15306534  0.42281695 
2  0.05513516  0.47795211 
3  0.03050646  0.50845857 
4  0.02064444  0.52910301 

Answer 1

应该是可以解决的开窗功能，假设你的PostgreSQL 8.4或更高版本。我猜total_statuses是沿select sum(frequency) from statuses_count_tmp行的视图或临时表？我写它作为一个CTE这里应该使计算结果只是一次对语句的持续时间：

with total_statuses as (select sum(frequency) from statuses_count_tmp) 
select statuses_count, 
     frequency/(select * from total_statuses) as frequency, 
     sum(frequency) over(order by statuses_count) 
     /(select * from total_statuses) as cumulative_frequency 
from statuses_count_tmp 

没有8.4的窗口功能，最好的办法是简单地处理重复数据：

create type cumulative_sum_type as (statuses_count int, frequency numeric, cumulative_frequency numeric); 
create or replace function cumulative_sum() returns setof cumulative_sum_type strict stable language plpgsql as $$ 
declare 
    running_total bigint := 0; 
    total bigint; 
    data_in record; 
    data_out cumulative_sum_type; 
begin 
    select sum(frequency) into total from statuses_count_tmp; 
    for data_in in select statuses_count, frequency from statuses_count_tmp order by statuses_count 
    loop 
    data_out.statuses_count := data_in.statuses_count; 
    running_total := running_total + data_in.frequency; 
    data_out.frequency = data_in.frequency::numeric/total; 
    data_out.cumulative_frequency = running_total::numeric/total; 
    return next data_out; 
    end loop; 
end; 
$$; 
select * from cumulative_sum();