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.sql.fun;
  
  import java.lang.annotation.ElementType;
  import java.lang.annotation.Retention;
  import java.lang.annotation.RetentionPolicy;
  import java.lang.annotation.Target;
  
  /**
   * An annotation that is read by {@link SqlLibraryOperatorTableFactory} to
   * add functions and operators to a library.
   *
   * <p>Typically, such collections are associated with a particular dialect or
   * database. For example, {@link SqlLibrary#ORACLE} is a collection of functions
   * that are in the Oracle database but not the SQL standard.
   *
   * <p>In {@link SqlLibraryOperatorTableFactory} this annotation is applied to
   * function definitions to include them in a particular library. It allows
   * an operator to belong to more than one library.
   */
  @Retention(RetentionPolicy.RUNTIME)
  @Target(ElementType.FIELD)
  public @interface LibraryOperator {
  
    /** The set of libraries that this function or operator belongs to.
     * Must not be null or empty. */
    SqlLibrary[] libraries();
  
    /** The set of libraries that this function should be excluded from.
     *
     * <p>Only needed when a library inherits functions from another library.
     * For example, {@link SqlLibrary#REDSHIFT} inherits from
     * {@link SqlLibrary#POSTGRESQL}, and therefore contains all of PostgreSQL's
     * operators by default. The {@code STARTS_WITH} function is in BigQuery and
     * PostgreSQL but not in Redshift and therefore has the annotation
     *
     * <blockquote>
     *   <pre>@LibraryOperator(libraries = {BIG_QUERY, POSTGRESQL},
     *   exceptLibraries = {REDSHIFT})</pre>
     * </blockquote>
     */
    SqlLibrary[] exceptLibraries() default {};
  }
  