Hello Krzysztof, The rewrite you mention in Hive was done in HIVE-19674 <https://issues.apache.org/jira/browse/HIVE-19674> to be able to push such group by to Druid. Currently there is no way to disable this rewrite.
As for removing Group by <constant>, there are rules/rewrites which can reduce grouping keys by removing constants but removing whole group by is not safe since it can lead to semantically different query. e.g. Select count(*) from empty_table group by <constant> will produce NULL but Select count(*) from empty_table will produce 0. P.S. There was a bug in HIVE-19674' patch which was further fixed by HIVE-21539 <https://issues.apache.org/jira/browse/HIVE-21539>. Regards, Vineet Garg On Wed, Jun 26, 2019 at 7:08 AM Haisheng Yuan <h.y...@alibaba-inc.com> wrote: > Calcite has the rule that does the work. But you can't remove the group by > clause if the constant is the only group key. The semantic is different > without group key. Try it on empty relation, you will see the difference. > > > > > > Thanks~ > Haisheng > Yuan------------------------------------------------------------------ > 发件人：Krzysztof Zarzycki<k.zarzy...@gmail.com> > 日 期：2019年06月26日 21:52:41 > 收件人：<dev@calcite.apache.org> > 主 题：Modify Calcite Planner in Hive to remove GROUP BY <constant> > > Hello, > > While the question I have might look like regards to Hive, I believe is > more about Calcite. I need to add a Calcite plan rule to Hive, that removes > "Group by" clause when it groups by some constant value (GROUP BY TRUE more > precisely). As far as I believe, the query semantically is the same. > Could anyone on this mailing list help me how to do it properly? While I'm > an experienced java engineer, I have no clue how to achieve this. > I was trying to modify hive code to do this myself, but unfortunately I got > only NullPointerExceptions. > > > More context below: > I want to use JdbcStorageHandler in Hive, that connects to Apache Kylin and > forward queries there. Then I put Tableau on top of Hive. Unfortunately, > the queries produced by Tableau to Hive and then reproduced by Calcite > Planner to Kylin, cannot be handled by Kylin (which BTW uses Calcite as > well). I disabled some of the hive optimizations which fixed some of my > queries. But I'm stuck on one I cannot disable. Tableau generates a query > with "GROUP BY 1.000000...01" , that is translated to "GROUP BY TRUE", by > Hive/Calcite. But neither of those can be handled by Kylin. I got an idea > that I will remove GROUP BY completely, because in my understanding it's > unecessary. > > I will be very grateful for your help, > Kind Regards, > Krzysztof > >
