query_optimizer/expressions/Scalar.hpp

/**
 *   Copyright 2011-2015 Quickstep Technologies LLC.
 *   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.
 **/

#ifndef QUICKSTEP_QUERY_OPTIMIZER_EXPRESSIONS_SCALAR_HPP_
#define QUICKSTEP_QUERY_OPTIMIZER_EXPRESSIONS_SCALAR_HPP_

#include <memory>
#include <unordered_map>

#include "query_optimizer/expressions/Expression.hpp"
#include "query_optimizer/expressions/ExprId.hpp"
#include "utility/Macros.hpp"

namespace quickstep {

class CatalogAttribute;
class Scalar;

namespace optimizer {
namespace expressions {

/** \addtogroup OptimizerExpressions
 *  @{
 */

class Scalar;
typedef std::shared_ptr<const Scalar> ScalarPtr;

/**
 * @brief Scalar expression that returns a single value based on input values
 *        that are not across multiple rows in an input relation.
 */
class Scalar : public Expression {
 public:
  ~Scalar() override {}

  /**
   * @brief Converts this expression to an expression for evaluation (in
   *        quickstep execution expressions system under /expressions)
   *        with each attribute reference being replaced by a CatalogAttribute
   *        reference provided in \p substitution_map.
   *
   * @param substitution_map Map from ExprId to CatalogAttribute for use in
   *                         substituting CatalogAttribute for
   *                         AttributeReference.
   * @return Concretized expression for evaluation.
   */
  virtual ::quickstep::Scalar* concretize(
      const std::unordered_map<ExprId, const CatalogAttribute*>& substitution_map)
      const = 0;

 protected:
  Scalar() {}

 private:
  DISALLOW_COPY_AND_ASSIGN(Scalar);
};

/** @} */

}  // namespace expressions
}  // namespace optimizer
}  // namespace quickstep

#endif /* QUICKSTEP_QUERY_OPTIMIZER_EXPRESSIONS_SCALAR_HPP_ */