void MergingSortedBlockInputStream::init(MutableColumns & merged_columns)
{
/// Read the first blocks, initialize the queue.
if (first)
{
first = false;
for (size_t i = 0; i < source_blocks.size(); ++i)
{
SharedBlockPtr & shared_block_ptr = source_blocks[i];
if (shared_block_ptr.get())
continue;
shared_block_ptr = new detail::SharedBlock(children[i]->read());
const size_t rows = shared_block_ptr->rows();
if (rows == 0)
continue;
if (expected_block_size < rows)
expected_block_size = std::min(rows, max_block_size);
cursors[i] = SortCursorImpl(*shared_block_ptr, description, i);
shared_block_ptr->all_columns = cursors[i].all_columns;
shared_block_ptr->sort_columns = cursors[i].sort_columns;
has_collation |= cursors[i].has_collation;
}
if (has_collation)
initQueue(queue_with_collation);
else
initQueue(queue_without_collation);
}
/// Let's check that all source blocks have the same structure.
for (const SharedBlockPtr & shared_block_ptr : source_blocks)
{
if (!*shared_block_ptr)
continue;
assertBlocksHaveEqualStructure(*shared_block_ptr, header, getName());
}
merged_columns.resize(num_columns);
for (size_t i = 0; i < num_columns; ++i)
{
merged_columns[i] = header.safeGetByPosition(i).column->cloneEmpty();
merged_columns[i]->reserve(expected_block_size);
}
}
void MergingSortedBlockInputStream::init(Block & merged_block, ColumnPlainPtrs & merged_columns)
{
/// Читаем первые блоки, инициализируем очередь.
if (first)
{
first = false;
size_t i = 0;
for (auto it = source_blocks.begin(); it != source_blocks.end(); ++it, ++i)
{
SharedBlockPtr & shared_block_ptr = *it;
if (shared_block_ptr.get())
continue;
shared_block_ptr = new detail::SharedBlock(children[i]->read());
if (shared_block_ptr->rowsInFirstColumn() == 0)
continue;
if (!num_columns)
num_columns = shared_block_ptr->columns();
cursors[i] = SortCursorImpl(*shared_block_ptr, description, i);
has_collation |= cursors[i].has_collation;
}
if (has_collation)
initQueue(queue_with_collation);
else
initQueue(queue);
}
/// Инициализируем результат.
/// Клонируем структуру первого непустого блока источников.
{
auto it = source_blocks.cbegin();
for (; it != source_blocks.cend(); ++it)
{
const SharedBlockPtr & shared_block_ptr = *it;
if (*shared_block_ptr)
{
merged_block = shared_block_ptr->cloneEmpty();
break;
}
}
/// Если все входные блоки пустые.
if (it == source_blocks.cend())
return;
}
/// Проверим, что у всех блоков-источников одинаковая структура.
for (auto it = source_blocks.cbegin(); it != source_blocks.cend(); ++it)
{
const SharedBlockPtr & shared_block_ptr = *it;
if (!*shared_block_ptr)
continue;
size_t src_columns = shared_block_ptr->columns();
size_t dst_columns = merged_block.columns();
if (src_columns != dst_columns)
throw Exception("Merging blocks has different number of columns", ErrorCodes::NUMBER_OF_COLUMNS_DOESNT_MATCH);
for (size_t i = 0; i < src_columns; ++i)
if (shared_block_ptr->getByPosition(i).name != merged_block.getByPosition(i).name
|| shared_block_ptr->getByPosition(i).type->getName() != merged_block.getByPosition(i).type->getName()
|| shared_block_ptr->getByPosition(i).column->getName() != merged_block.getByPosition(i).column->getName())
throw Exception("Merging blocks has different names or types of columns", ErrorCodes::BLOCKS_HAS_DIFFERENT_STRUCTURE);
}
for (size_t i = 0; i < num_columns; ++i)
merged_columns.emplace_back(merged_block.getByPosition(i).column.get());
}