Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/2811#discussion_r88433730
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/plan/rules/dataSet/DataSetSingleRowCrossRule.scala
---
@@ -0,0 +1,88 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.flink.api.table.plan.rules.dataSet
+
+import org.apache.calcite.plan.volcano.RelSubset
+import org.apache.calcite.plan.{Convention, RelOptRule, RelOptRuleCall,
RelTraitSet}
+import org.apache.calcite.rel.RelNode
+import org.apache.calcite.rel.convert.ConverterRule
+import org.apache.calcite.rel.logical.{LogicalAggregate, LogicalJoin}
+import org.apache.flink.api.table.plan.nodes.dataset.{DataSetConvention,
DataSetSingleRowCross}
+
+class DataSetSingleRowCrossRule
+ extends ConverterRule(
+ classOf[LogicalJoin],
+ Convention.NONE,
+ DataSetConvention.INSTANCE,
+ "DataSetSingleRowCrossRule") {
+
+ override def matches(call: RelOptRuleCall): Boolean = {
+ val join = call.rel(0).asInstanceOf[LogicalJoin]
+
+ if (isCrossJoin(join)) {
+
isGlobalAggregation(join.getRight.asInstanceOf[RelSubset].getOriginal) ||
+
isGlobalAggregation(join.getLeft.asInstanceOf[RelSubset].getOriginal)
+ } else {
+ false
+ }
+ }
+
+ private def isCrossJoin(join: LogicalJoin) = {
+ val joinCondition = join.analyzeCondition.pairs()
+ joinCondition.isEmpty
+ }
+
+ private def isGlobalAggregation(node: RelNode) = {
+ node.isInstanceOf[LogicalAggregate] &&
+ isSingleLine(node.asInstanceOf[LogicalAggregate])
+ }
+
+ private def isSingleLine(agg: LogicalAggregate) = {
+ agg.getGroupSet.isEmpty
+ }
+
+ override def convert(rel: RelNode): RelNode = {
+ val join = rel.asInstanceOf[LogicalJoin]
+ val traitSet = rel.getTraitSet.replace(DataSetConvention.INSTANCE)
+ val (singleRowNode, multiRowNode) =
placeSingleRowNodeFirst(join.getLeft, join.getRight)
--- End diff --
We cannot simply switch the join inputs. Calcite expects the result of the
join to be `fields-of-first-input ++ fields-of-second-input`. Hence, the
`DataSetSingleCross` needs to know, which on was the original first input or we
keep the inputs in the current order and tell `DataSetSingleCross` which one is
the input with the single row. I'd prefer the second option.
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