[CALCITE-4743] Convert rel to sql fail, when meeting aggregate of no-group and no-aggcall.

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: core
• Assignee: Unassigned
• Reporter: Xurenhe
• Created: 17/Aug/21 12:30
• Updated: 30/Aug/21 11:40

Description

Hi, all.
Here, Aggregate of of no-group and no-agg-call coverting to sql is fail.
For example:

  @Test void testAggregateWithNoGroupAndNoAggCall() {
    final RelBuilder builder = relBuilder();
    final RelNode relRoot = builder.scan("EMP")
        .aggregate(builder.groupKey())
        .project(ImmutableList.of(builder.literal("hello")), ImmutableList.of("constant_field"))
        .build();

    String expected = "SELECT 'hello' AS \"constant_field\"\n"
        + "FROM \"scott\".\"EMP\"";
    relFn(b -> relRoot).ok(expected);
  }

This case will return sql:

SELECT 'hello' AS "constant_field"
FROM "scott"."EMP"
GROUP BY ()

--------------------------------------
Should we use a switch of dialect to control this conversion, which is code of `org.apache.calcite.rel.rel2sql.RelToSqlConverter#buildAggregate`?

Issue Links

• is related to: CALCITE-4597 Allow RelNodes to have an empty row type (zero fields)