xiaoming, Kylin saves the HyperLogLog or Bitmap for the distinct count measure (not just a number!), which means they are mergable for complex query. So even you mark A+B+C as mandantory, when you query for a certain sub combination like A, it will use those HLL or Bitmap to merge again to return what you want.
2016-11-17 14:18 GMT+08:00 张晓明（zhangxiaoming）-技术产品中心 <zhangxiaom...@qiyi.com >: > Thanks Billy > > If Kylin save the result separate By A B C,The Times Can be understand, > But “count distinct ” is merge the same “u” ,Can’t do ++ Operation > “” > > > > *From:* Billy(Yiming) Liu [mailto:liuyiming....@gmail.com] > *Sent:* Thursday, November 17, 2016 2:05 PM > *To:* user <u...@kylin.apache.org> > *Cc:* dev@kylin.apache.org > *Subject:* Re: some confuse about Mandatory Dimensions > > > > If you set A, B, and C as mandatory dimensions, that means Kylin will save > the cuboid result by grouping A, B, C internally. But that not means you > could only query by grouping A, B, C. If you only query A, B. The final > result will do post-aggregation by grouping the above cuboid. Same as query > grouping A. The cost is performance, since more post-aggregation needed. > But if you query by grouping D. There would be no result, since you missed > the mandatory dimension. > > > > 2016-11-17 13:31 GMT+08:00 张晓明（zhangxiaoming）-技术产品中心 < > zhangxiaom...@qiyi.com>: > > Hi,all > > I have create a cube in My System with Mandatory Dimensions such > as A B C, and the Measure use count distinct filed “u” will HLL , > > When the segment of the cube complete,I query the result with kylin sql > as “select count(distinct u) from table where A=xxx and b=yyy” or “select > count(distinct u) from table where A=xxx ”. The result is correct > > In my opinion, all of the query condition must be set (A=xxx,B=yyyy,C=zzz) > ,the kylin sql can be wrok, > > The question is How the Kylin query the result and the distinct value is > right ? that is unbelievable > > > > > > -- > > With Warm regards > > Yiming Liu (刘一鸣) > -- Best regards, Shaofeng Shi 史少锋
