org.apache.calcite.sql2rel.DeduplicateCorrelateVariables.java Source code

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Here is the source code for org.apache.calcite.sql2rel.DeduplicateCorrelateVariables.java

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/*
 * 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.sql2rel;

import org.apache.calcite.rel.RelHomogeneousShuttle;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.core.CorrelationId;
import org.apache.calcite.rex.RexBuilder;
import org.apache.calcite.rex.RexCorrelVariable;
import org.apache.calcite.rex.RexNode;
import org.apache.calcite.rex.RexShuttle;
import org.apache.calcite.rex.RexSubQuery;

import com.google.common.collect.ImmutableSet;

/**
 * Rewrites relations to ensure the same correlation is referenced by the same
 * correlation variable.
 */
public class DeduplicateCorrelateVariables extends RelHomogeneousShuttle {
    private final RexShuttle dedupRex;

    /** Creates a DeduplicateCorrelateVariables. */
    private DeduplicateCorrelateVariables(RexBuilder builder, CorrelationId canonicalId,
            ImmutableSet<CorrelationId> alternateIds) {
        dedupRex = new DeduplicateCorrelateVariablesShuttle(builder, canonicalId, alternateIds, this);
    }

    /**
     * Rewrites a relational expression, replacing alternate correlation variables
     * with a canonical correlation variable.
     */
    public static RelNode go(RexBuilder builder, CorrelationId canonicalId,
            Iterable<? extends CorrelationId> alternateIds, RelNode r) {
        return r.accept(new DeduplicateCorrelateVariables(builder, canonicalId, ImmutableSet.copyOf(alternateIds)));
    }

    @Override
    public RelNode visit(RelNode other) {
        RelNode next = super.visit(other);
        return next.accept(dedupRex);
    }

    /**
     * Replaces alternative names of correlation variable to its canonical name.
     */
    private static class DeduplicateCorrelateVariablesShuttle extends RexShuttle {
        private final RexBuilder builder;
        private final CorrelationId canonicalId;
        private final ImmutableSet<CorrelationId> alternateIds;
        private final DeduplicateCorrelateVariables shuttle;

        private DeduplicateCorrelateVariablesShuttle(RexBuilder builder, CorrelationId canonicalId,
                ImmutableSet<CorrelationId> alternateIds, DeduplicateCorrelateVariables shuttle) {
            this.builder = builder;
            this.canonicalId = canonicalId;
            this.alternateIds = alternateIds;
            this.shuttle = shuttle;
        }

        @Override
        public RexNode visitCorrelVariable(RexCorrelVariable variable) {
            if (!alternateIds.contains(variable.id)) {
                return variable;
            }

            return builder.makeCorrel(variable.getType(), canonicalId);
        }

        @Override
        public RexNode visitSubQuery(RexSubQuery subQuery) {
            if (shuttle != null) {
                RelNode r = subQuery.rel.accept(shuttle); // look inside sub-queries
                if (r != subQuery.rel) {
                    subQuery = subQuery.clone(r);
                }
            }
            return super.visitSubQuery(subQuery);
        }
    }
}

// End DeduplicateCorrelateVariables.java