ClickHouse/dbms/src/DataStreams/AggregatingSortedBlockInputStream.h

#pragma once

#include <common/logger_useful.h>

#include <Core/Row.h>
#include <Core/ColumnNumbers.h>
#include <DataStreams/MergingSortedBlockInputStream.h>
#include <AggregateFunctions/IAggregateFunction.h>
#include <Columns/ColumnAggregateFunction.h>


namespace DB
{

/** Merges several sorted streams to one.
  * During this for each group of consecutive identical values of the primary key (the columns by which the data is sorted),
  * merges them into one row. When merging, the data is pre-aggregated - merge of states of aggregate functions,
  * corresponding to a one value of the primary key. For columns that are not part of the primary key and which do not have the AggregateFunction type,
  * when merged, the first value is selected.
  */
class AggregatingSortedBlockInputStream : public MergingSortedBlockInputStream
{
public:
    AggregatingSortedBlockInputStream(BlockInputStreams inputs_, const SortDescription & description_, size_t max_block_size_)
        : MergingSortedBlockInputStream(inputs_, description_, max_block_size_)
    {
    }

    String getName() const override { return "AggregatingSorted"; }

    String getID() const override
    {
        std::stringstream res;
        res << "AggregatingSorted(inputs";

        for (size_t i = 0; i < children.size(); ++i)
            res << ", " << children[i]->getID();

        res << ", description";

        for (size_t i = 0; i < description.size(); ++i)
            res << ", " << description[i].getID();

        res << ")";
        return res.str();
    }

    bool isGroupedOutput() const override { return true; }
    bool isSortedOutput() const override { return true; }
    const SortDescription & getSortDescription() const override { return description; }

protected:
    /// Can return 1 more records than max_block_size.
    Block readImpl() override;

private:
    Logger * log = &Logger::get("AggregatingSortedBlockInputStream");

    /// Read finished.
    bool finished = false;

    /// Columns with which numbers should be aggregated.
    ColumnNumbers column_numbers_to_aggregate;
    ColumnNumbers column_numbers_not_to_aggregate;
    std::vector<ColumnAggregateFunction *> columns_to_aggregate;

    RowRef current_key;        /// The current primary key.
    RowRef next_key;           /// The primary key of the next row.

    /** We support two different cursors - with Collation and without.
     *  Templates are used instead of polymorphic SortCursor and calls to virtual functions.
     */
    void merge(MutableColumnRawPtrs & merged_columns, std::priority_queue<TSortCursor> & queue);

    /** Extract all states of aggregate functions and merge them with the current group.
      */
    void addRow(TSortCursor & cursor);
};

}