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;
  
  /**
   * Describes when a function/operator will return null.
   *
   * <p>STRICT and ANY are similar. STRICT says f(a0, a1) will NEVER return
   * null if a0 and a1 are not null. This means that we can check whether f
   * returns null just by checking its arguments. Use STRICT in preference to
   * ANY whenever possible.
   */
  public enum NullPolicy {
    /** Returns null if and only if all of the arguments are null;
     * If all of the arguments are false return false otherwise true. */
    ALL,
    /** Returns null if and only if one of the arguments are null. */
    STRICT,
    /** Returns null if one of the arguments is null, and possibly other times. */
    SEMI_STRICT,
    /** If any of the arguments are null, return null. */
    ANY,
    /** If the first argument is null, return null. */
    ARG0,
    NONE
  }
  