Hi Yuan, Sorry, there is a typo in the last mail: inconsistent -> consistent
Yours, Weihao Li At 2024-08-29 10:06:23, "Weihao Li" <18110526...@163.com> wrote: >Hi Yuan, > >I think it is good to be inconsistent with the behavior of relational >databases. If we only get one row when query select s2, s3 from root.db.d1, >user cannot distinguish between the following two cases: > >1. The device has no data in other time; > >2. The device has data in other time, just these selected sensors has no data. > > > > >Yours, > >Weihao Li > > > > > > > > > > > >At 2024-08-29 09:45:07, "Yuan Tian" <jackietie...@gmail.com> wrote: >>Hi all, >> >>If you are familiar with the tree model, you should know that for a device >>d1, if it contains three sensors: s1, s2, s3, and its data are like: >>Time | s1 | s2 | s3 | >>-------|-----|-----|-----| >>1 | 1| 10|100 | >>-------|-----|-----|-----| >>2 | 2| null|null | >>-------|-----|-----|-----| >>3 | 3| null|null | >> >> >>if we only query s2 and s3, select s2, s3 from root.db.d1, we will only get >>one row(the first row), because for 2 and 3 row, s2 and s3 are all null, >>we automatically filter out rows that are entirely null during a scan by >>the storage engine. >> >>However, this is inconsistent with the behavior of relational databases >>which will return all three rows. So in our table model, should we keep >>consistent with tree model, or we follow the relational databases way? >>Personally, I think that we should maintain consistency with relational >>databases. >> >>What do you think? >> >>Best regards, >>---------------------- Yuan Tian
