[CALCITE-4560] Wrong plan when decorrelating EXISTS subquery with COA…

…LESCE in the predicate

1. Add plan transformations before starting the core RelDecorrelator logic
to bring the plan into an equivalent but more convenient form that can be
decorrelated into more efficient and correct plans.

2. Based on the changes above many plans with subqueries become more
efficient since the value generator is no longer necessary and it is dropped.

3. Add test cases in SqlToRelConverter, subquery.iq reproducing the
problem (bad plan/query results) and update existing tests based on the
changes.

Close #2406

core/src/main/java/org/apache/calcite/rel/rules/FilterFlattenCorrelatedConditionRule.java

@@ -0,0 +1,146 @@
+/*
+ * 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 org.apiguardian.api.API;
+
+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.
+ *
+ * <p>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.</p>
+ *
+ * <p>Sub-plan before</p>
+ * <pre>
+ * LogicalProject($f0=[true])
+ *   LogicalFilter(condition=[=($cor0.DEPTNO, +($7, 30))])
+ *     LogicalTableScan(table=[[CATALOG, SALES, EMP]])
+ * </pre>
+ *
+ * <p>Sub-plan after</p>
+ * <pre>
+ * LogicalProject($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>
+ *
+ * <p>The rule should be used in conjunction with other rules and transformations to have a positive
+ * impact on the plan. At the moment it is tightly connected with the decorrelation logic and may
+ * not be useful in a broader context. Projects may implement decorrelation differently so they may
+ * choose to use this rule or not.</p>
+ */
+@API(since = "1.27", status = API.Status.EXPERIMENTAL)
+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<>();
+    // Visitor logic strongly dependent on RelDecorrelator#findCorrelationEquivalent
+    // Handling more kinds of expressions may be useless if the respective logic cannot exploit them
+    RexNode newCondition = filter.getCondition().accept(new RexShuttle() {
+      @Override public RexNode visitCall(RexCall call) {
+        switch (call.getKind()) {
+        case EQUALS:
+        case NOT_EQUALS:
+        case GREATER_THAN:
+        case GREATER_THAN_OR_EQUAL:
+        case LESS_THAN:
+        case LESS_THAN_OR_EQUAL:
+        case IS_DISTINCT_FROM:
+        case IS_NOT_DISTINCT_FROM:
+          RexNode op0 = call.operands.get(0);
+          RexNode op1 = call.operands.get(1);
+          final int replaceIndex;
+          if (RexUtil.containsCorrelation(op1) && isUncorrelatedCall(op0)) {
+            replaceIndex = 0;
+          } else if (RexUtil.containsCorrelation(op0) && isUncorrelatedCall(op1)) {
+            replaceIndex = 1;
+          } else {
+            // Structure does not match, do not replace
+            replaceIndex = -1;
+          }
+          if (replaceIndex != -1) {
+            List<RexNode> copyOperands = new ArrayList<>(call.operands);
+            RexNode oldOp = call.operands.get(replaceIndex);
+            RexNode newOp = b.getRexBuilder()
+                .makeInputRef(oldOp.getType(), proj + projOperands.size());
+            projOperands.add(oldOp);
+            copyOperands.set(replaceIndex, newOp);
+            return call.clone(call.type, copyOperands);
+          }
+          return call;
+        case AND:
+        case OR:
+          return super.visitCall(call);
+        default:
+          return call;
+        }
+      }
+    });
+    if (newCondition.equals(filter.getCondition())) {
+      return;
+    }
+    b.projectPlus(projOperands);
+    b.filter(newCondition);
+    b.project(b.fields(ImmutableBitSet.range(proj).asList()));
+    call.transformTo(b.build());
+  }
+
+  private static boolean isUncorrelatedCall(RexNode node) {
+    return node instanceof RexCall && !RexUtil.containsCorrelation(node);
+  }
+
+  /** Rule configuration. */
+  public interface Config extends RelRule.Config {
+    Config DEFAULT =
+        EMPTY.withOperandSupplier(op -> op.operand(Filter.class).anyInputs()).as(Config.class);
+
+    @Override default FilterFlattenCorrelatedConditionRule toRule() {
+      return new FilterFlattenCorrelatedConditionRule(this);
+    }
+  }
+}