[GitHub] [druid] gianm commented on a change in pull request #10324: SQL support for union datasources.

[GitBox <gi...@apache.org>]

gianm commented on a change in pull request #10324:
URL: https://github.com/apache/druid/pull/10324#discussion_r478507597



##########
File path: sql/src/main/java/org/apache/druid/sql/calcite/rule/DruidUnionDataSourceRule.java
##########
@@ -0,0 +1,157 @@
+/*
+ * 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.druid.sql.calcite.rule;
+
+import com.google.common.base.Preconditions;
+import org.apache.calcite.plan.RelOptRule;
+import org.apache.calcite.plan.RelOptRuleCall;
+import org.apache.calcite.rel.RelNode;
+import org.apache.calcite.rel.core.Union;
+import org.apache.calcite.util.mapping.Mappings;
+import org.apache.druid.query.TableDataSource;
+import org.apache.druid.segment.column.RowSignature;
+import org.apache.druid.sql.calcite.rel.DruidQueryRel;
+import org.apache.druid.sql.calcite.rel.DruidRel;
+import org.apache.druid.sql.calcite.rel.DruidRels;
+import org.apache.druid.sql.calcite.rel.DruidUnionDataSourceRel;
+import org.apache.druid.sql.calcite.rel.PartialDruidQuery;
+import org.apache.druid.sql.calcite.table.DruidTable;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+/**
+ * Creates a {@link DruidUnionDataSourceRel} from various {@link DruidQueryRel} inputs that represent simple
+ * table scans.
+ */
+public class DruidUnionDataSourceRule extends RelOptRule
+{
+  private static final DruidUnionDataSourceRule INSTANCE = new DruidUnionDataSourceRule();
+
+  private DruidUnionDataSourceRule()
+  {
+    super(
+        operand(
+            Union.class,
+            operand(DruidRel.class, none()),
+            operand(DruidQueryRel.class, none())
+        )
+    );
+  }
+
+  public static DruidUnionDataSourceRule instance()
+  {
+    return INSTANCE;
+  }
+
+  @Override
+  public boolean matches(RelOptRuleCall call)
+  {
+    final Union unionRel = call.rel(0);
+    final DruidRel<?> firstDruidRel = call.rel(1);
+    final DruidQueryRel secondDruidRel = call.rel(2);
+
+    // Can only do UNION ALL of inputs that have compatible schemas (or schema mappings).
+    return unionRel.all && isUnionCompatible(firstDruidRel, secondDruidRel);
+  }
+
+  @Override
+  public void onMatch(final RelOptRuleCall call)
+  {
+    final Union unionRel = call.rel(0);
+    final DruidRel<?> firstDruidRel = call.rel(1);
+    final DruidQueryRel secondDruidRel = call.rel(2);
+
+    if (firstDruidRel instanceof DruidUnionDataSourceRel) {
+      // Unwrap and flatten the inputs to the Union.
+      final RelNode newUnionRel = call.builder()
+                                      .pushAll(firstDruidRel.getInputs())
+                                      .push(secondDruidRel)
+                                      .union(true, firstDruidRel.getInputs().size() + 1)
+                                      .build();
+
+      call.transformTo(
+          DruidUnionDataSourceRel.create(
+              (Union) newUnionRel,
+              getColumnNamesIfTableOrUnion(firstDruidRel).get(),
+              firstDruidRel.getQueryMaker()
+          )
+      );
+    } else {
+      // Sanity check.
+      Preconditions.checkState(firstDruidRel instanceof DruidQueryRel);

Review comment:
       I added a message.




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