Hi, yes, root is like "/" in Unix-like OS. ----------------------------------- Xiangdong Huang School of Software, Tsinghua University
黄向东 清华大学 软件学院 Dhruv Garg <[email protected]> 于2021年3月8日周一 下午6:14写道： > Hello Xiangdong, > > Thanks for confirming! One last question for now, all storage groups must > start with "root" right? I cannot have storage groups like root1.demo, > correct? > > Regards, > dgargcs > > On Mon, 8 Mar 2021 at 15:37, Xiangdong Huang <[email protected]> wrote: > > > Hi Dhruv, > > > > Yes you are right. and IoTDB also supports join on timestamp across > > storage groups. > > > > Q2: IoTDB does not support that now. > > Current join looks like outer-join in RDBMS. > > Supporting left join, right join and inner-join is not hard to implement, > > just omit the rows that contain NULL. > > (Better implementation will need CBO cost-based optimization, but IoTDB > > lacks the statistics info for that.) > > > > Best, > > ----------------------------------- > > Xiangdong Huang > > School of Software, Tsinghua University > > > > 黄向东 > > 清华大学 软件学院 > > > > > > Dhruv Garg <[email protected]> 于2021年3月8日周一 下午5:56写道： > > > > > Hello Xiangdong, > > > > > > Yes. Let me elaborate a bit about the join requirement. Suppose I want > to > > > do a join to print out values in root.demo.d1.m1 and root.demo.d2.m2 > for > > a > > > common time range say 2019-12-11 00:00:00 to 2020-12-18 23:59:59. It > > should > > > print out the last two rows from your table. > > > > > > In SQL, when we do a join, there are two different tables and then we > do > > a > > > join based on some common column => root.demo.d1 is one table (has an > > "m1" > > > column) and another table root.demo.d2 (has an "m2" column). If I do a > > join > > > on d1 and d2 based on timestamp, it will return some rows containing m1 > > and > > > m2 where timestamps are the same. > > > > > > I think the way to look at join queries in IoTDB is slightly different. > > > Here, we have a storage group (root.demo) with different time-series > > (d1.m1 > > > and d2.m2). For each insert in a storage group, I think IoTDB > > automatically > > > joins these time-series on timestamp since it assumes null values for > > other > > > time-series that were not given a value during insert. For example, > if I > > > do an "insert root.demo.d2(timestamp,m2) values (2021-08-03T00:00:00, > > > 2021)", it will also append NULL value for root.demo.d1.m1 for this > > > timestamp. > > > > > > Thus, to do a join within a storage group for *any number* of > time-series > > > is straightforward. I think this is trivially done by just giving the > > time > > > range and time-series names => "select d1.m1, d2.m2 from root.demo > where > > > timestamp >= 2019-19-11T00:00:00". > > > > > > Next, I thought about a similar query across storage groups, say > > root.demo1 > > > and root.demo2. Here as well, I can run a similar query, but only start > > > from a higher level in the storage hierarchy, i.e. "root" alone. > "select > > > demo1.m1, demo2.m2 from root where timestamp >= 2019-19-11T00:00:00". > > > > > > Q1. Is my interpretation of join on timestamp correct for IoTDB? > > > > > > Q2. Is there a way to omit rows that return one or more null column > > values > > > in the result? > > > > > > PS: Sorry for the long email. I am exploring IoTDB for a research > project > > > and just want to be clear in my understanding. > > > > > > Thanks in advance! > > > > > > Regards, > > > dgargcs > > > > > > On Mon, 8 Mar 2021 at 14:12, Xiangdong Huang <[email protected]> > wrote: > > > > > > > Hi Dhruv, > > > > > > > > 1. Could you give me an example to describe what you want to query? > > > > e.g., there are two time series: > > > > > > > > +-----------------------------+---------------+---------------+ > > > > | Time|root.demo.d1.m1|root.demo.d2.m2| > > > > +-----------------------------+---------------+---------------+ > > > > |1970-01-01T08:00:00.001+08:00| 1.0| 2.0| > > > > |2019-12-11T10:00:00.000+08:00| 1.0| NULL| > > > > |2020-12-18T11:45:14.519+08:00| 2.0| 2.0| > > > > +-----------------------------+---------------+---------------+ > > > > > > > > or, > > > > > > > > What you want to query? (you can consider it as a table in MySQL, and > > > just > > > > write the sqls you need in mysql.) > > > > > > > > 2. Ah, we are testing the performance of v0.12. maybe 2-3 weeks, I > > think. > > > > > > > > Best, > > > > ----------------------------------- > > > > Xiangdong Huang > > > > School of Software, Tsinghua University > > > > > > > > 黄向东 > > > > 清华大学 软件学院 > > > > > > > > > > > > Dhruv Garg <[email protected]> 于2021年3月8日周一 下午4:11写道： > > > > > > > > > Hello Xiangdong, > > > > > > > > > > Thanks for your response. > > > > > > > > > > 1. I have the same use-case: I want to run a join query on two time > > > > > series but I think I am getting the syntax wrong. > > > > > I tried a few SQL-like join queries on IoTDB v0.11.2 and got the > > > > following > > > > > error: "mismatched input 'JOIN' expecting {<EOF>, WHERE, ORDER, > > > SLIMIT, > > > > > LIMIT, OFFSET, SOFFSET, FILL, GROUP, DISABLE, ALIGN, ',', '.'}" > > > > > Could you please refer me to some documentation or provide a simple > > > > example > > > > > join query for IoTDB? > > > > > > > > > > 2. I am also excited to try out the cluster version. Is there an > > > > > approximate timeline for v0.12 rollout? > > > > > > > > > > Thanks in advance. > > > > > > > > > > Regards, > > > > > dgargcs > > > > > > > > > > On Tue, 2 Mar 2021 at 17:24, Xiangdong Huang <[email protected]> > > > wrote: > > > > > > > > > > > Hi Dhruv, > > > > > > > > > > > > Welcome! > > > > > > > > > > > > 1. "join" for what requirements? > > > > > > > > > > > > IoTDB supports JOIN two time series ON their timestamp, i.e., > time > > > > series > > > > > > alignment. > > > > > > > > > > > > 2. I think the cluster version is coming... In the coming v0.12, > I > > > > think > > > > > a > > > > > > cluster version (that does > > > > > > not support dynamically scale-out) will be released, and the > > > scale-out > > > > > > feature may be released in v0.13 or 0.14. > > > > > > > > > > > > Best, > > > > > > ----------------------------------- > > > > > > Xiangdong Huang > > > > > > School of Software, Tsinghua University > > > > > > > > > > > > Dhruv Garg <[email protected]> 于2021年3月2日周二 下午3:54写道： > > > > > > > > > > > > > Hello, > > > > > > > > > > > > > > I am a researcher and a new user of IoTDB. I was excited when I > > saw > > > > the > > > > > > > performance numbers of IoTDB compared to InfluxDB, and I have > set > > > it > > > > up > > > > > > on > > > > > > > a few workstations and a Raspberry Pi device. > > > > > > > > > > > > > > I am becoming familiar with it and have a few queries: > > > > > > > > > > > > > > 1. Does IoTDB support Join queries? - I tried looking up > some > > > > > > > documentation on it, but could not find any. If the feature > is > > > > > > > available, > > > > > > > could you please provide a sample query or the predicates > for > > > join > > > > > > > queries? > > > > > > > 2. I also browsed through the IoTDB Jira issues page. I saw > > that > > > > the > > > > > > > distributed / cluster version is being developed. > > Approximately > > > > how > > > > > > much > > > > > > > time would it take to get a stable / working version of the > > > > cluster > > > > > > > IoTDB? > > > > > > > > > > > > > > It would be great if someone can respond to my queries. I would > > be > > > > > > > waiting for a reply. Thanks in advance. > > > > > > > > > > > > > > Regards, > > > > > > > dgargcs > > > > > > > > > > > > > > > > > > > > > > > > > > > >
