在Oracle中創建直方圖/頻率分佈的最佳方法？

Question

我有一個events表，其中有兩列eventkey（唯一主鍵）和createtime，它將事件的創建時間存儲爲NUMBER列中1970年1月1日以來的毫秒數。

我想創建一個「直方圖」或頻率分佈，顯示在過去一週的每個小時內創建了多少個事件。

這是使用width_bucket()函數在Oracle中編寫此類查詢的最佳方法嗎？是否有可能使用其他Oracle分析函數之一推導出落入每個存儲桶的行數，而不是使用width_bucket來確定每行所屬的存儲分區數量，並在此基礎上執行count(*)？

-- 1305504000000 = 5/16/2011 12:00am GMT 
-- 1306108800000 = 5/23/2011 12:00am GMT 
select 
timestamp '1970-01-01 00:00:00' + numtodsinterval((1305504000000/1000 + (bucket * 60 * 60)), 'second') period_start, 
numevents 
from (
    select bucket, count(*) as events from (
    select eventkey, createtime, 
    width_bucket(createtime, 1305504000000, 1306108800000, 24 * 7) bucket 
    from events 
    where createtime between 1305504000000 and 1306108800000 
) group by bucket 
) 
order by period_start 

Answer 1

如果您createtime是一個日期列，這將是微不足道的：

SELECT TO_CHAR(CREATE_TIME, 'DAY:HH24'), COUNT(*) 
    FROM EVENTS 
GROUP BY TO_CHAR(CREATE_TIME, 'DAY:HH24'); 

因爲它是，鑄造createtime列不是太難：

select TO_CHAR( 
     TO_DATE('19700101', 'YYYYMMDD') + createtime/86400000), 
     'DAY:HH24') AS BUCKET, COUNT(*) 
    FROM EVENTS 
    WHERE createtime between 1305504000000 and 1306108800000 
group by TO_CHAR( 
     TO_DATE('19700101', 'YYYYMMDD') + createtime/86400000), 
     'DAY:HH24') 
order by 1 

---

如果您正在尋找fencepost值（例如，我從哪裏開始第一個十分位數（0-10％ ）到下（11-20％），你會做這樣的事情：

select min(createtime) over (partition by decile) as decile_start, 
     max(createtime) over (partition by decile) as decile_end, 
     decile 
    from (select createtime, 
       ntile (10) over (order by createtime asc) as decile 
      from events 
     where createtime between 1305504000000 and 1306108800000 
     ) 

Answer 2

我不熟悉Oracle的日期函數，但我敢肯定有寫這篇聲明的Postgres的等效方式：

select date_trunc('hour', stamp), count(*) 
from your_data 
group by date_trunc('hour', stamp) 
order by date_trunc('hour', stamp) 

Answer 3

差不多亞當相同的反應，但我寧願如果需要保持period_start爲時間字段，以便更容易進一步篩選：

with 
events as 
(
    select rownum eventkey, round(dbms_random.value(1305504000000, 1306108800000)) createtime 
    from dual 
    connect by level <= 1000 
) 
select 
    trunc(timestamp '1970-01-01 00:00:00' + numtodsinterval(createtime/1000, 'second'), 'HH') period_start, 
    count(*) numevents 
from 
    events 
where 
    createtime between 1305504000000 and 1306108800000 
group by 
    trunc(timestamp '1970-01-01 00:00:00' + numtodsinterval(createtime/1000, 'second'), 'HH') 
order by 
    period_start