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.rel.stream;
  
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.RelInput;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.SingleRel;
  import org.apache.calcite.rel.core.TableScan;
  
  /**
   * Relational operator that converts a relation to a stream.
   *
   * <p>For example, if {@code Orders} is a table, and {@link TableScan}(Orders)
   * is a relational operator that returns the current contents of the table,
   * then {@link Delta}(TableScan(Orders)) is a relational operator that returns
   * all inserts into the table.
   *
   * <p>If unrestricted, Delta returns all previous inserts into the table (from
   * time -&infin; to now) and all future inserts into the table (from now
   * to +&infin;) and never terminates.
   */
  public abstract class Delta extends SingleRel {
    protected Delta(RelOptCluster cluster, RelTraitSet traits, RelNode input) {
      super(cluster, traits, input);
    }
  
    /** Creates a Delta by parsing serialized output. */
    protected Delta(RelInput input) {
      this(input.getCluster(), input.getTraitSet(), input.getInput());
    }
  }
  