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

/*
 * 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.RelOptCluster;
import org.apache.calcite.plan.RelOptRuleCall;
import org.apache.calcite.plan.RelRule;
import org.apache.calcite.rel.RelCollations;
import org.apache.calcite.rel.core.Aggregate;
import org.apache.calcite.rel.core.AggregateCall;
import org.apache.calcite.rel.core.Project;
import org.apache.calcite.rel.type.RelDataType;
import org.apache.calcite.rel.type.RelDataTypeFactory;
import org.apache.calcite.rex.RexBuilder;
import org.apache.calcite.rex.RexCall;
import org.apache.calcite.rex.RexLiteral;
import org.apache.calcite.rex.RexNode;
import org.apache.calcite.sql.SqlKind;
import org.apache.calcite.sql.SqlPostfixOperator;
import org.apache.calcite.sql.fun.SqlStdOperatorTable;
import org.apache.calcite.sql.type.SqlTypeName;
import org.apache.calcite.tools.RelBuilder;
import org.apache.calcite.tools.RelBuilderFactory;

import com.google.common.collect.ImmutableList;

import org.checkerframework.checker.nullness.qual.Nullable;
import org.immutables.value.Value;

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;

/**
 * Rule that converts CASE-style filtered aggregates into true filtered
 * aggregates.
 *
 * <p>For example,
 *
 * <blockquote>
 *   <code>SELECT SUM(CASE WHEN gender = 'F' THEN salary END)<br>
 *   FROM Emp</code>
 * </blockquote>
 *
 * <p>becomes
 *
 * <blockquote>
 *   <code>SELECT SUM(salary) FILTER (WHERE gender = 'F')<br>
 *   FROM Emp</code>
 * </blockquote>
 *
 * @see CoreRules#AGGREGATE_CASE_TO_FILTER
 */
@Value.Enclosing
public class AggregateCaseToFilterRule
    extends RelRule<AggregateCaseToFilterRule.Config>
    implements TransformationRule {

  /** Creates an AggregateCaseToFilterRule. */
  protected AggregateCaseToFilterRule(Config config) {
    super(config);
  }

  @Deprecated // to be removed before 2.0
  protected AggregateCaseToFilterRule(RelBuilderFactory relBuilderFactory,
      String description) {
    this(Config.DEFAULT.withRelBuilderFactory(relBuilderFactory)
        .withDescription(description)
        .as(Config.class));
  }

  @Override public boolean matches(final RelOptRuleCall call) {
    final Aggregate aggregate = call.rel(0);
    final Project project = call.rel(1);

    for (AggregateCall aggregateCall : aggregate.getAggCallList()) {
      final int singleArg = soleArgument(aggregateCall);
      if (singleArg >= 0
          && isThreeArgCase(project.getProjects().get(singleArg))) {
        return true;
      }
    }

    return false;
  }

  @Override public void onMatch(RelOptRuleCall call) {
    final Aggregate aggregate = call.rel(0);
    final Project project = call.rel(1);
    final List<AggregateCall> newCalls =
        new ArrayList<>(aggregate.getAggCallList().size());
    final List<RexNode> newProjects = new ArrayList<>(project.getProjects());

    for (AggregateCall aggregateCall : aggregate.getAggCallList()) {
      AggregateCall newCall =
          transform(aggregateCall, project, newProjects);

      if (newCall == null) {
        newCalls.add(aggregateCall);
      } else {
        newCalls.add(newCall);
      }
    }

    if (newCalls.equals(aggregate.getAggCallList())) {
      return;
    }

    final RelBuilder relBuilder = call.builder()
        .push(project.getInput())
        .project(newProjects);

    final RelBuilder.GroupKey groupKey =
        relBuilder.groupKey(aggregate.getGroupSet(), aggregate.getGroupSets());

    relBuilder.aggregate(groupKey, newCalls)
        .convert(aggregate.getRowType(), false);

    call.transformTo(relBuilder.build());
    call.getPlanner().prune(aggregate);
  }

  private static @Nullable AggregateCall transform(AggregateCall aggregateCall,
      Project project, List<RexNode> newProjects) {
    final int singleArg = soleArgument(aggregateCall);
    if (singleArg < 0) {
      return null;
    }

    final RexNode rexNode = project.getProjects().get(singleArg);
    if (!isThreeArgCase(rexNode)) {
      return null;
    }

    final RelOptCluster cluster = project.getCluster();
    final RexBuilder rexBuilder = cluster.getRexBuilder();
    final RexCall caseCall = (RexCall) rexNode;

    // If one arg is null and the other is not, reverse them and set "flip",
    // which negates the filter.
    final boolean flip = RexLiteral.isNullLiteral(caseCall.operands.get(1))
        && !RexLiteral.isNullLiteral(caseCall.operands.get(2));
    final RexNode arg1 = caseCall.operands.get(flip ? 2 : 1);
    final RexNode arg2 = caseCall.operands.get(flip ? 1 : 2);

    // Operand 1: Filter
    final SqlPostfixOperator op =
        flip ? SqlStdOperatorTable.IS_NOT_TRUE : SqlStdOperatorTable.IS_TRUE;
    final RexNode filterFromCase =
        rexBuilder.makeCall(op, caseCall.operands.get(0));

    // Combine the CASE filter with an honest-to-goodness SQL FILTER, if the
    // latter is present.
    final RexNode filter;
    if (aggregateCall.filterArg >= 0) {
      filter = rexBuilder.makeCall(SqlStdOperatorTable.AND,
          project.getProjects().get(aggregateCall.filterArg), filterFromCase);
    } else {
      filter = filterFromCase;
    }

    final SqlKind kind = aggregateCall.getAggregation().getKind();
    if (aggregateCall.isDistinct()) {
      // Just one style supported:
      //   COUNT(DISTINCT CASE WHEN x = 'foo' THEN y END)
      // =>
      //   COUNT(DISTINCT y) FILTER(WHERE x = 'foo')

      if (kind == SqlKind.COUNT
          && RexLiteral.isNullLiteral(arg2)) {
        newProjects.add(arg1);
        newProjects.add(filter);
        return AggregateCall.create(SqlStdOperatorTable.COUNT, true, false,
            false, ImmutableList.of(newProjects.size() - 2),
            newProjects.size() - 1, null, RelCollations.EMPTY,
            aggregateCall.getType(), aggregateCall.getName());
      }
      return null;
    }

    // Four styles supported:
    //
    // A1: AGG(CASE WHEN x = 'foo' THEN cnt END)
    //   => operands (x = 'foo', cnt, null)
    // A2: SUM(CASE WHEN x = 'foo' THEN cnt ELSE 0 END)
    //   => operands (x = 'foo', cnt, 0); must be SUM
    // B: SUM(CASE WHEN x = 'foo' THEN 1 ELSE 0 END)
    //   => operands (x = 'foo', 1, 0); must be SUM
    // C: COUNT(CASE WHEN x = 'foo' THEN 'dummy' END)
    //   => operands (x = 'foo', 'dummy', null)

    if (kind == SqlKind.COUNT // Case C
        && arg1.isA(SqlKind.LITERAL)
        && !RexLiteral.isNullLiteral(arg1)
        && RexLiteral.isNullLiteral(arg2)) {
      newProjects.add(filter);
      return AggregateCall.create(SqlStdOperatorTable.COUNT, false, false,
          false, ImmutableList.of(), newProjects.size() - 1, null,
          RelCollations.EMPTY, aggregateCall.getType(),
          aggregateCall.getName());
    } else if (kind == SqlKind.SUM // Case B
        && isIntLiteral(arg1, BigDecimal.ONE)
        && isIntLiteral(arg2, BigDecimal.ZERO)) {

      newProjects.add(filter);
      final RelDataTypeFactory typeFactory = cluster.getTypeFactory();
      final RelDataType dataType =
          typeFactory.createTypeWithNullability(
              typeFactory.createSqlType(SqlTypeName.BIGINT), false);
      return AggregateCall.create(SqlStdOperatorTable.COUNT, false, false,
          false, ImmutableList.of(), newProjects.size() - 1, null,
          RelCollations.EMPTY, dataType, aggregateCall.getName());
    } else if ((RexLiteral.isNullLiteral(arg2) // Case A1
            && aggregateCall.getAggregation().allowsFilter())
        || (kind == SqlKind.SUM // Case A2
            && isIntLiteral(arg2, BigDecimal.ZERO))) {
      newProjects.add(arg1);
      newProjects.add(filter);
      return AggregateCall.create(aggregateCall.getAggregation(), false,
          false, false, ImmutableList.of(newProjects.size() - 2),
          newProjects.size() - 1, null, RelCollations.EMPTY,
          aggregateCall.getType(), aggregateCall.getName());
    } else {
      return null;
    }
  }

  /** Returns the argument, if an aggregate call has a single argument,
   * otherwise -1. */
  private static int soleArgument(AggregateCall aggregateCall) {
    return aggregateCall.getArgList().size() == 1
        ? aggregateCall.getArgList().get(0)
        : -1;
  }

  private static boolean isThreeArgCase(final RexNode rexNode) {
    return rexNode.getKind() == SqlKind.CASE
        && ((RexCall) rexNode).operands.size() == 3;
  }

  private static boolean isIntLiteral(RexNode rexNode, BigDecimal value) {
    return rexNode instanceof RexLiteral
        && SqlTypeName.INT_TYPES.contains(rexNode.getType().getSqlTypeName())
        && value.equals(((RexLiteral) rexNode).getValueAs(BigDecimal.class));
  }

  /** Rule configuration. */
  @Value.Immutable
  public interface Config extends RelRule.Config {
    Config DEFAULT = ImmutableAggregateCaseToFilterRule.Config.of()
        .withOperandSupplier(b0 ->
            b0.operand(Aggregate.class).oneInput(b1 ->
                b1.operand(Project.class).anyInputs()));


    @Override default AggregateCaseToFilterRule toRule() {
      return new AggregateCaseToFilterRule(this);
    }
  }
}