RemoveAggregateEmptyGrandTotalRule.java

/*
 * Copyright 2016 Imply Data, Inc.
 *
 * Licensed 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 io.druid.sql.calcite.rule;

import com.google.common.base.Predicates;
import com.google.common.collect.ImmutableList;
import org.apache.calcite.plan.RelOptRule;
import org.apache.calcite.plan.RelOptRuleCall;
import org.apache.calcite.rel.core.Aggregate;
import org.apache.calcite.rel.core.AggregateCall;
import org.apache.calcite.rel.core.Values;
import org.apache.calcite.rel.logical.LogicalValues;
import org.apache.calcite.rex.RexBuilder;
import org.apache.calcite.rex.RexLiteral;
import org.apache.calcite.sql.SqlKind;

import java.math.BigDecimal;

/**
 * Rule that removes a grand-total Aggregate (no grouping keys) on an empty Values.
 *
 * Useful because Calcite's built-in PruneEmptyRules doesn't do this. Sample query where this matters:
 * <code>SELECT COUNT(*) FROM s.foo WHERE 1 = 0</code>.
 */
public class RemoveAggregateEmptyGrandTotalRule extends RelOptRule
{
  private static final RemoveAggregateEmptyGrandTotalRule INSTANCE = new RemoveAggregateEmptyGrandTotalRule();

  private RemoveAggregateEmptyGrandTotalRule()
  {
    super(
        operand(
            Aggregate.class,
            null,
            Predicates.not(Aggregate.IS_NOT_GRAND_TOTAL),
            operand(Values.class, null, Values.IS_EMPTY, none())
        )
    );
  }

  public static RemoveAggregateEmptyGrandTotalRule instance()
  {
    return INSTANCE;
  }

  @Override
  public void onMatch(RelOptRuleCall call)
  {
    final Aggregate aggregate = call.rel(0);
    final Values values = call.rel(1);

    final ImmutableList.Builder<RexLiteral> literals = ImmutableList.builder();

    final RexBuilder rexBuilder = call.builder().getRexBuilder();
    for (final AggregateCall aggregateCall : aggregate.getAggCallList()) {
      final SqlKind kind = aggregateCall.getAggregation().getKind();
      if (kind == SqlKind.COUNT || kind == SqlKind.SUM0) {
        literals.add((RexLiteral) rexBuilder.makeLiteral(BigDecimal.ZERO, aggregateCall.getType(), false));
      } else {
        literals.add(rexBuilder.constantNull());
      }
    }

    call.transformTo(
        LogicalValues.create(
            values.getCluster(),
            aggregate.getRowType(),
            ImmutableList.of(literals.build())
        )
    );
  }
}