content: /*
   * 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.adapter.enumerable;
  
  /**
   * Implements a windowed aggregate function by generating expressions to
   * initialize, add to, and get a result from, an accumulator.
   * Windowed aggregate is more powerful than regular aggregate since it can
   * access rows in the current partition by row indices.
   * Regular aggregate can be used to implement windowed aggregate.
   *
   * <p>This interface does not define new methods: window-specific
   * sub-interfaces are passed when implementing window aggregate.
   *
   * @see org.apache.calcite.adapter.enumerable.StrictWinAggImplementor
   * @see org.apache.calcite.adapter.enumerable.RexImpTable.FirstLastValueImplementor
   * @see org.apache.calcite.adapter.enumerable.RexImpTable.RankImplementor
   * @see org.apache.calcite.adapter.enumerable.RexImpTable.RowNumberImplementor
   */
  public interface WinAggImplementor extends AggImplementor {
    /**
     * Allows to access rows in window partition relative to first/last and
     * current row.
     */
    enum SeekType {
      /**
       * Start of window.
       *
       * @see WinAggFrameContext#startIndex()
       */
      START,
      /**
       * Row position in the frame.
       *
       * @see WinAggFrameContext#index()
       */
      SET,
      /**
       * The index of row that is aggregated.
       * Valid only in {@link WinAggAddContext}.
       *
       * @see WinAggAddContext#currentPosition()
       */
      AGG_INDEX,
      /**
       * End of window.
       *
       * @see WinAggFrameContext#endIndex()
       */
      END
    }
  
    boolean needCacheWhenFrameIntact();
  }
  