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.plan;
  
  /**
   * The mode of trait derivation.
   */
  public enum DeriveMode {
    /**
     * Uses the left most child's traits to decide what
     * traits to require from the other children. This
     * generally applies to most operators.
     */
    LEFT_FIRST,
  
    /**
     * Uses the right most child's traits to decide what
     * traits to require from the other children. Operators
     * like index nested loop join may find this useful.
     */
    RIGHT_FIRST,
  
    /**
     * Iterates over each child, uses current child's traits
     * to decide what traits to require from the other
     * children. It includes both LEFT_FIRST and RIGHT_FIRST.
     * System that doesn't enable join commutativity should
     * consider this option. Special customized operators
     * like a Join who has 3 inputs may find this useful too.
     */
    BOTH,
  
    /**
     * Leave it to you, you decide what you cook. This will
     * allow planner to pass all the traits from all the
     * children, the user decides how to make use of these
     * traits and whether to derive new rel nodes.
     */
    OMAKASE,
  
    /**
     * Trait derivation is prohibited.
     */
    PROHIBITED
  }
  