expressions/aggregation/AggregateFunctionCount.cpp

/**
 *   Copyright 2015 Pivotal Software, 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.
 **/

#include "expressions/aggregation/AggregateFunctionCount.hpp"

#include <vector>

#include "expressions/aggregation/AggregationHandleCount.hpp"
#include "types/Type.hpp"
#include "types/TypeFactory.hpp"
#include "types/TypeID.hpp"

#include "glog/logging.h"

namespace quickstep {

bool AggregateFunctionCount::canApplyToTypes(
    const std::vector<const Type*> &argument_types) const {
  // COUNT may be nullary (i.e. COUNT(*)) or unary.
  return argument_types.size() <= 1;
}

const Type* AggregateFunctionCount::resultTypeForArgumentTypes(
    const std::vector<const Type*> &argument_types) const {
  if (!canApplyToTypes(argument_types)) {
    return nullptr;
  }

  return &TypeFactory::GetType(kLong);
}

AggregationHandle* AggregateFunctionCount::createHandle(
    const std::vector<const Type*> &argument_types) const {
  DCHECK(canApplyToTypes(argument_types))
      << "Attempted to create an AggregationHandleCount for argument Types "
      << "that COUNT can not be applied to (> 1 argument).";

  if (argument_types.empty()) {
    // COUNT(*)
    return new AggregationHandleCount<true, false>();
  } else if (argument_types.front()->isNullable()) {
    // COUNT(some_nullable_argument)
    return new AggregationHandleCount<false, true>();
  } else {
    // COUNT(non_nullable_argument)
    //
    // TODO(chasseur): Modify query optimizer to optimize-away COUNT with a
    // non-nullable argument and convert it to COUNT(*).
    return new AggregationHandleCount<false, false>();
  }
}

}  // namespace quickstep