我有一个事件表,其中包含两列eventkey(唯一,主键)和createtime,它将事件的创建时间存储为NUMBER列中自1970年1月1日以来的毫秒数.
我想创建一个“直方图”或频率分布,显示过去一周每小时创建了多少事件.
这是使用width_bucket()函数在Oracle中编写此类查询的最佳方法吗？是否可以使用其他Oracle分析函数之一导出落入每个存储桶的行数,而不是使用width_bucket来确定每行所属的存储桶编号并对其进行计数(*)？
-- 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
解决方法
如果您的创建时间是日期列,那么这将是微不足道的：
SELECT TO_CHAR(CREATE_TIME,'DAY:HH24'),COUNT(*) FROM EVENTS GROUP BY TO_CHAR(CREATE_TIME,'DAY:HH24');
实际上,转换createtime列并不太难：
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','DAY:HH24')
order by 1
或者,如果您正在寻找fencepost值(例如,从第一个十分位数(0-10％)到下一个十分位数(11-20％),您可以执行以下操作：
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
)
