Question regarding ProjectRemoveRule

[Shuyi Chen]

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."