Apache Calcite 使用关系表达式使用关联变量（关联子查询）

org.apache.calcite.test.RelBuilderTest

  @Test public void testCorrelationWithCondition() {
    final RelBuilder builder = RelBuilder.create(config().build());
    final Holder<RexCorrelVariable> v = Holder.of(null);
    RelNode root = builder.scan("EMP")
        .variable(v)
        .scan("DEPT")
        .filter(
            builder.equals(builder.field(0),
                builder.field(v.get(), "DEPTNO")))
        .join(JoinRelType.LEFT,
            builder.equals(builder.field(2, 0, "SAL"),
                builder.literal(1000)),
            ImmutableSet.of(v.get().id))
        .build();
    // Note that the join filter gets pushed to the right-hand input of
    // LogicalCorrelate
    final String expected = ""
        + "LogicalCorrelate(correlation=[$cor0], joinType=[left], requiredColumns=[{7}])\n"
        + "  LogicalTableScan(table=[[scott, EMP]])\n"
        + "  LogicalFilter(condition=[=($cor0.SAL, 1000)])\n"
        + "    LogicalFilter(condition=[=($0, $cor0.DEPTNO)])\n"
        + "      LogicalTableScan(table=[[scott, DEPT]])\n";
    assertThat(root, hasTree(expected));
  }

  @Test public void testCorrelationFails() {
    final RelBuilder builder = RelBuilder.create(config().build());
    final Holder<RexCorrelVariable> v = Holder.of(null);
    try {
      builder.scan("EMP")
          .variable(v)
          .filter(builder.equals(builder.field(0), v.get()))
          .scan("DEPT")
          .join(JoinRelType.INNER, builder.literal(true),
              ImmutableSet.of(v.get().id));
      fail("expected error");
    } catch (IllegalArgumentException e) {
      assertThat(e.getMessage(),
          containsString("variable $cor0 must not be used by left input to correlation"));
    }
  }