text: // 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.
  
  #ifndef DORIS_BE_SRC_QUERY_EXEC_MERGE_NODE_H
  #define DORIS_BE_SRC_QUERY_EXEC_MERGE_NODE_H
  
  #include "exec/exec_node.h"
  #include "runtime/mem_pool.h"
  
  namespace doris {
  
  class Tuple;
  class TupleRow;
  
  // Node that merges the results of its children by materializing their
  // evaluated expressions into row batches. The MergeNode pulls row batches sequentially
  // from its children sequentially, i.e., it exhausts one child completely before moving
  // on to the next one.
  class MergeNode : public ExecNode {
  public:
      MergeNode(ObjectPool* pool, const TPlanNode& tnode, const DescriptorTbl& descs);
      virtual ~MergeNode() {}
  
      // Create const exprs, child exprs and conjuncts from corresponding thrift exprs.
      virtual Status init(const TPlanNode& tnode, RuntimeState* state = nullptr);
      virtual Status prepare(RuntimeState* state);
      virtual Status open(RuntimeState* state);
      virtual Status get_next(RuntimeState* state, RowBatch* row_batch, bool* eos);
      virtual Status close(RuntimeState* state);
  
  private:
      const static int INVALID_CHILD_IDX = -1;
  
      // Tuple id resolved in prepare() to set _tuple_desc;
      int _tuple_id;
  
      // Descriptor for tuples this merge node constructs.
      const TupleDescriptor* _tuple_desc;
  
      // those tuple_desc_->slots() which are materialized, in the same order
      std::vector<SlotDescriptor*> _materialized_slots;
  
      // Const exprs materialized by this node. These exprs don't refer to any children.
      std::vector<std::vector<ExprContext*>> _const_result_expr_ctx_lists;
  
      // Exprs materialized by this node. The i-th result expr list refers to the i-th child.
      std::vector<std::vector<ExprContext*>> _result_expr_ctx_lists;
  
      // Index of current const result expr list.
      int _const_result_expr_idx;
  
      // Index of current child.
      int _child_idx;
  
      // Current row batch of current child. We reset the pointer to a new RowBatch
      // when switching to a different child.
      std::unique_ptr<RowBatch> _child_row_batch;
  
      // Saved from the last to get_next() on the current child.
      bool _child_eos;
  
      // Index of current row in _child_row_batch.
      int _child_row_idx;
  
      // Evaluates exprs on all rows in _child_row_batch starting from _child_row_idx,
      // and materializes their results into *tuple.
      // Adds *tuple into row_batch, and increments *tuple.
      // If const_exprs is true, then the exprs are evaluated exactly once without
      // fetching rows from _child_row_batch.
      // Only commits tuples to row_batch if they are not filtered by conjuncts.
      // Returns true if row_batch should be returned to caller or limit has been
      // reached, false otherwise.
      bool eval_and_materialize_exprs(const std::vector<ExprContext*>& exprs, bool const_exprs,
                                      Tuple** tuple, RowBatch* row_batch);
  };
  
  } // namespace doris
  
  #endif
  