[GitHub] [calcite] zabetak commented on a change in pull request #2406: [CALCITE-4560]: Wrong plan when decorrelating EXISTS subquery with COALESCE in the predicate

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zabetak commented on a change in pull request #2406:
URL: https://github.com/apache/calcite/pull/2406#discussion_r622240277



##########
File path: core/src/main/java/org/apache/calcite/rel/rules/FilterFlattenCorrelatedConditionRule.java
##########
@@ -0,0 +1,134 @@
+/*
+ * 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.calcite.rel.rules;
+
+import org.apache.calcite.plan.RelOptRuleCall;
+import org.apache.calcite.plan.RelRule;
+import org.apache.calcite.rel.core.Filter;
+import org.apache.calcite.rex.RexCall;
+import org.apache.calcite.rex.RexNode;
+import org.apache.calcite.rex.RexShuttle;
+import org.apache.calcite.rex.RexUtil;
+import org.apache.calcite.tools.RelBuilder;
+import org.apache.calcite.util.ImmutableBitSet;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Planner rule that matches a {@link Filter} expression with correlated variables, and rewrites the
+ * condition in a simpler form that is more convenient for the decorrelation logic.
+ *
+ * Uncorrelated calls below a comparison operator are turned into input references by extracting the
+ * computation in a {@link org.apache.calcite.rel.core.Project} expression. An additional projection
+ * may be added on top of the new filter to retain expression equivalence.
+ *
+ * Sub-plan before
+ * <pre>
+ * LogicalProject($f0=[true])
+ *   LogicalFilter(condition=[=($cor0.DEPTNO, +($7, 30))])
+ *     LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+ * </pre>
+ *
+ * Sub-plan after
+ * <pre>
+ * LogicalProject($f0=[true])
+ *   LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2],..., COMM=[$6], DEPTNO=[$7], SLACKER=[$8])
+ *     LogicalFilter(condition=[=($cor0.DEPTNO, $9)])
+ *       LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2],..., SLACKER=[$8], $f9=[+($7, 30)])
+ *         LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+ * </pre>
+ */
+public final class FilterFlattenCorrelatedConditionRule
+    extends RelRule<FilterFlattenCorrelatedConditionRule.Config> {
+
+  public FilterFlattenCorrelatedConditionRule(final Config config) {
+    super(config);
+  }
+
+  @Override public boolean matches(RelOptRuleCall call) {
+    Filter filter = call.rel(0);
+    return RexUtil.containsCorrelation(filter.getCondition());
+  }
+
+  @Override public void onMatch(RelOptRuleCall call) {
+    Filter filter = call.rel(0);
+    RelBuilder b = call.builder();
+    b.push(filter.getInput());
+    final int proj = b.fields().size();
+    List<RexNode> projOperands = new ArrayList<>();
+    RexNode newCondition = filter.getCondition().accept(new RexShuttle() {
+      @Override public RexNode visitCall(RexCall call) {
+        switch (call.getKind()) {
+        case EQUALS:

Review comment:
       Makes sense, although it will not make a huge difference for Calcite itself.




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