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;
  
  import org.apache.calcite.rel.core.AggregateCall;
  import org.apache.calcite.rex.RexBuilder;
  import org.apache.calcite.rex.RexNode;
  import org.apache.calcite.util.ImmutableBitSet;
  
  import com.google.common.collect.ImmutableList;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /** Aggregate function whose value may be a constant expression, based on
   * only the contents of the GROUP BY clause. */
  public interface SqlStaticAggFunction {
    /** Generates an expression for the aggregate function; or null if the value
     * is not constant.
     *
     * <p>For example:
     * <ul>
     *   <li>{@code GROUPING(deptno)} expands to literal {@code 0}
     *       if the aggregate has {@code GROUP BY deptno}
     * </ul>
     *
     * @param rexBuilder Rex builder
     * @param groupSet Group set
     * @param groupSets Group sets
     * @param aggregateCall Aggregate call
     *
     * @return Expression for single row
     */
    @Nullable RexNode constant(RexBuilder rexBuilder, ImmutableBitSet groupSet,
        ImmutableList<ImmutableBitSet> groupSets, AggregateCall aggregateCall);
  }
  