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.validate;
  
  import org.apache.calcite.sql.SqlNode;
  
  /**
   * An extension to the {@link SqlValidatorScope} interface which indicates that
   * the scope is aggregating.
   *
   * <p>A scope which is aggregating must implement this interface. Such a scope
   * will return the same set of identifiers as its parent scope, but some of
   * those identifiers may not be accessible because they are not in the GROUP BY
   * clause.
   */
  public interface AggregatingScope extends SqlValidatorScope {
    //~ Methods ----------------------------------------------------------------
  
    /**
     * Checks whether an expression is constant within the GROUP BY clause. If
     * the expression completely matches an expression in the GROUP BY clause,
     * returns true. If the expression is constant within the group, but does
     * not exactly match, returns false. If the expression is not constant,
     * throws an exception. Examples:
     *
     * <ul>
     * <li>If we are 'f(b, c)' in 'SELECT a + f(b, c) FROM t GROUP BY a', then
     * the whole expression matches a group column. Return true.
     * <li>Just an ordinary expression in a GROUP BY query, such as 'f(SUM(a),
     * 1, b)' in 'SELECT f(SUM(a), 1, b) FROM t GROUP BY b'. Returns false.
     * <li>Illegal expression, such as 'f(5, a, b)' in 'SELECT f(a, b) FROM t
     * GROUP BY a'. Throws when it enounters the 'b' operand, because it is not
     * in the group clause.
     * </ul>
     */
    boolean checkAggregateExpr(SqlNode expr, boolean deep);
  }
  