Thanks a lot, Julian. I was actually looking at the this code block in
ProjectRemoveRule, it's actually trying to preserve the rename info of the
top project (see the if block), so it may actually produce something like
the following:
LogicalAggregate(group=[{0}])
LogicalProject(departmentNo=[$7])
LogicalTableScan(table=[[scott, EMP]])
public void onMatch(RelOptRuleCall call) {
Project project = call.rel(0);
assert isTrivial(project);
RelNode stripped = project.getInput();
if (stripped instanceof Project) {
// Rename columns of child projection if desired field names are given.
Project childProject = (Project) stripped;
stripped = childProject.copy(childProject.getTraitSet(),
childProject.getInput(), childProject.getProjects(),
project.getRowType());
}
RelNode child = call.getPlanner().register(stripped, project);
call.transformTo(child);
}
However, "stripped" is a RelSubset which contains a Project during the
volcano planner optimization. So the if () code block won't be executed. Do
you think we can fix this to make it work again? Thanks a lot.
Shuyi
On Thu, Jan 18, 2018 at 3:54 PM, Julian Hyde <jh...@apache.org> wrote:
> Planner rules do their best to keep field names the same, but they don’t
> guarantee it. If they did, they’d miss a lot of good opportunities to
> optimize.
>
> By the way, the same goes for RelBuilder.
>
> Julian
>
>
> > On Jan 18, 2018, at 3:50 PM, Shuyi Chen <suez1...@gmail.com> wrote:
> >
> > Hi,
> >
> > I have a question regarding the ProjectRemoveRule. In Calcite 1980, a
> test
> > case was introduced below:
> >
> > /** Test case for
> > * <a href="https://issues.apache.org/jira/browse/CALCITE-1980";>
> [CALCITE-1980]
> > * RelBuilder gives NPE if groupKey contains alias</a>.
> > *
> > * <p>Now, the alias does not cause a new expression to be added to the
> input,
> > * but causes the referenced fields to be renamed. */
> > @Test public void testAggregateProjectWithAliases() {
> > final RelBuilder builder = RelBuilder.create(config().build());
> > RelNode root =
> > builder.scan("EMP")
> > .project(builder.field("DEPTNO"))
> > .aggregate(
> > builder.groupKey(
> > builder.alias(builder.field("DEPTNO"),
> "departmentNo")))
> > .build();
> > final String expected = ""
> > + "LogicalAggregate(group=[{0}])\n"
> > + " LogicalProject(departmentNo=[$0])\n"
> > + " LogicalProject(DEPTNO=[$7])\n"
> > + " LogicalTableScan(table=[[scott, EMP]])\n";
> > assertThat(str(root), is(expected));
> > }
> >
> > So according the ProjectRemoveRule, which will remove the top project,
> the
> > above REL will be optimized as the following:
> >
> > LogicalAggregate(group=[{0}])
> > LogicalProject(DEPTNO=[$7])
> > LogicalTableScan(table=[[scott, EMP]])
> >
> > But this will lose rename information "departmentNo". Is this expected,
> and
> > is it a problem that should get fixed? Please correct me if I am wrong.
> > Thanks a lot.
> >
> > Shuyi
> > --
> > "So you have to trust that the dots will somehow connect in your future."
>
>
--
"So you have to trust that the dots will somehow connect in your future."
