thanks Greg, just subscribed to Jira updates. Boris
On Thu, Jun 27, 2019 at 5:37 PM Greg Rahn <greg.r...@gmail.com> wrote: > As you have observed, today, multiple references to a relation results in > multiple scans of the relation -- so that is the expected behavior. > > Most system that materialize CTEs with >1 reference to them do so via > temporary tables behind the scenes. That said, such functionality does not > exist in Impala today, but there is a JIRA for it: > https://issues.apache.org/jira/browse/IMPALA-8083 > > > > On Thu, Jun 27, 2019 at 9:50 AM Boris Tyukin <bo...@boristyukin.com> > wrote: > >> Hello, >> >> a lot of our SQL users love CTEs (Common Table Expressions), including >> myself. CTEs make code easier to read, maintain and normally have very good >> performance in traditional RDBMS like SQL Server or Oracle (and our SQL >> users happen to have a background with those systems). >> >> While CTEs work fine in Impala, it seems to me that Impala does not >> materialize CTEs temporarily, if CTE is used in more than one place in a >> query, and instead get expanded and all the joins repeated in every place >> CTE results are used. >> >> Is this expected behavior and is there any good hints (not hacks) to >> force Impala to materialize CTEs if they are used in several places in the >> same query? >> >> I did not find anything concerning CTE performance in Impala docs and >> only found this thread which does look to me like a hack than a solution >> >> https://community.cloudera.com/t5/Interactive-Short-cycle-SQL/Performance-Reduced-after-Removing-ORDER-BY-clause/td-p/28832 >> >> >> Thanks, >> Boris >> >
