gustavodemorais commented on code in PR #27733: URL: https://github.com/apache/flink/pull/27733#discussion_r2885039730
########## flink-table/flink-table-planner/src/main/java/org/apache/flink/table/planner/plan/rules/logical/SimplifyCoalesceWithEquiJoinConditionRule.java: ########## @@ -0,0 +1,302 @@ +/* + * 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.table.planner.plan.rules.logical; + +import org.apache.flink.annotation.Internal; +import org.apache.flink.table.functions.BuiltInFunctionDefinitions; +import org.apache.flink.table.planner.functions.bridging.BridgingSqlFunction; +import org.apache.flink.table.planner.plan.utils.FlinkRexUtil; + +import org.apache.calcite.plan.RelOptRuleCall; +import org.apache.calcite.plan.RelRule; +import org.apache.calcite.rel.RelNode; +import org.apache.calcite.rel.core.Calc; +import org.apache.calcite.rel.core.Join; +import org.apache.calcite.rel.core.JoinInfo; +import org.apache.calcite.rel.core.JoinRelType; +import org.apache.calcite.rel.core.Project; +import org.apache.calcite.rex.RexBuilder; +import org.apache.calcite.rex.RexCall; +import org.apache.calcite.rex.RexInputRef; +import org.apache.calcite.rex.RexNode; +import org.apache.calcite.rex.RexShuttle; +import org.apache.calcite.sql.SqlKind; +import org.apache.calcite.sql.SqlOperator; +import org.apache.calcite.util.mapping.IntPair; +import org.immutables.value.Value; + +import java.util.function.Predicate; + +/** + * Simplifies {@code COALESCE(b.k, a.k)} to the preserved-side column reference when the two + * arguments reference columns from opposite sides of an equi-join condition. + * + * <p>For a {@code LEFT JOIN a ON a.k = b.k}, {@code COALESCE(b.k, a.k)} always equals {@code a.k}: + * + * <ul> + * <li>When b matches: {@code b.k = a.k} (equi-join guarantees this), so the result is {@code + * a.k}. + * <li>When b doesn't match: {@code b.k} is NULL, so the result falls through to {@code a.k}. + * </ul> + * + * <p>Both orderings ({@code COALESCE(b.k, a.k)} and {@code COALESCE(a.k, b.k)}) resolve to the + * preserved-side key. This applies to LEFT, RIGHT, and INNER joins. FULL OUTER joins are not + * handled because both sides can generate nulls. + * + * <p>This rule matches a {@link Project} or {@link Calc} whose input is a {@link Join}. It uses a + * {@link RexShuttle} to recursively find and simplify applicable COALESCE calls, including those + * nested inside other expressions (e.g., {@code CAST(COALESCE(b.k, a.k) AS VARCHAR)}). + */ +@Internal [email protected] +public class SimplifyCoalesceWithEquiJoinConditionRule + extends RelRule<SimplifyCoalesceWithEquiJoinConditionRule.Config> { + + public static final RelRule<Config> PROJECT_INSTANCE = Config.DEFAULT.withProject().toRule(); + + public static final RelRule<Config> CALC_INSTANCE = Config.DEFAULT.withCalc().toRule(); + + public SimplifyCoalesceWithEquiJoinConditionRule(Config config) { + super(config); + } + + @Override + public void onMatch(RelOptRuleCall call) { + final RelNode relNode = call.rel(0); + final Join join = call.rel(1); + + final JoinInfo joinInfo = join.analyzeCondition(); + if (joinInfo.pairs().isEmpty()) { + return; + } + + final RexBuilder rexBuilder = join.getCluster().getRexBuilder(); + final int leftFieldCount = join.getLeft().getRowType().getFieldCount(); + + final EquiJoinCoalesceSimplifier shuttle = + new EquiJoinCoalesceSimplifier( + rexBuilder, joinInfo, join.getJoinType(), leftFieldCount); + + final RelNode transformed = relNode.accept(shuttle); + if (shuttle.isSimplified()) { + call.transformTo(transformed); + } + } + + // -------------------------------------------------------------------------------------------- + + /** + * A {@link RexShuttle} that replaces {@code COALESCE(refA, refB)} with the preserved-side + * column reference when the two arguments form an equi-join pair from opposite sides. + */ + private static class EquiJoinCoalesceSimplifier extends RexShuttle { + + private final RexBuilder rexBuilder; + private final JoinInfo joinInfo; + private final JoinRelType joinType; + private final int leftFieldCount; + private boolean simplified = false; + + private EquiJoinCoalesceSimplifier( + RexBuilder rexBuilder, + JoinInfo joinInfo, + JoinRelType joinType, + int leftFieldCount) { + this.rexBuilder = rexBuilder; + this.joinInfo = joinInfo; + this.joinType = joinType; + this.leftFieldCount = leftFieldCount; + } + + boolean isSimplified() { + return simplified; + } + + @Override + public RexNode visitCall(RexCall call) { + // Recurse first (bottom-up) so nested COALESCE calls are handled + call = (RexCall) super.visitCall(call); + + if (!operatorIsCoalesce(call.getOperator())) { + return call; + } + if (call.getOperands().size() != 2) { + return call; + } + + final RexNode op0 = call.getOperands().get(0); + final RexNode op1 = call.getOperands().get(1); + if (!(op0 instanceof RexInputRef) || !(op1 instanceof RexInputRef)) { + return call; + } + + final RexInputRef ref0 = (RexInputRef) op0; + final RexInputRef ref1 = (RexInputRef) op1; + + // Must be from opposite sides of the join + final boolean isLeft0 = ref0.getIndex() < leftFieldCount; + final boolean isLeft1 = ref1.getIndex() < leftFieldCount; + if (isLeft0 == isLeft1) { + return call; + } + + // Identify left-side and right-side refs + final int leftIdx = isLeft0 ? ref0.getIndex() : ref1.getIndex(); + final int rightIdx = (isLeft0 ? ref1.getIndex() : ref0.getIndex()) - leftFieldCount; + final RexInputRef leftRef = isLeft0 ? ref0 : ref1; + final RexInputRef rightRef = isLeft0 ? ref1 : ref0; + + // Check if they form an equi-join pair + if (!isEquiJoinPair(leftIdx, rightIdx)) { + return call; + } + + // Determine the preserved-side reference + final RexInputRef preservedRef = resolvePreservedSide(leftRef, rightRef, ref0); + if (preservedRef == null) { + return call; + } + + simplified = true; + + // Handle potential type mismatch by adding a CAST if needed + if (call.getType().equals(preservedRef.getType())) { Review Comment: done -- This is an automated message from the Apache Git Service. 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