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 > > > > > > > > > > > > > > >
