Function adaptBlockStructure

src/QueryPipeline/RemoteQueryExecutor.cpp:348–403

If we receive a block with slightly different column types, or with excessive columns, * we will adapt it to expected structure. */

  *  we will adapt it to expected structure.
  */
static Block adaptBlockStructure(const Block & block, const Block & header)
{
    /// Special case when reader doesn't care about result structure. Deprecated and used only in Benchmark, PerformanceTest.
    if (header.empty())
        return block;

    Block res;
    res.info = block.info;

    for (const auto & elem : header)
    {
        ColumnPtr column;

        if (elem.column && isColumnConst(*elem.column))
        {
            /// We expect constant column in block.
            /// If block is not empty, then get value for constant from it,
            /// because it may be different for remote server for functions like version(), uptime(), ...
            if (block.rows() > 0 && block.has(elem.name))
            {
                /// Const column is passed as materialized. Get first value from it.
                ///
                /// TODO: check that column contains the same value.
                /// TODO: serialize const columns.
                auto col = block.getByName(elem.name);
                if (const auto * blob = typeid_cast<const ColumnBLOB *>(col.column.get()))
                    col.column = blob->convertFrom();
                col.column = col.column->cut(0, 1);

                column = castColumn(col, elem.type);

                if (!isColumnConst(*column))
                    column = ColumnConst::create(column, block.rows());
                else
                    /// It is not possible now. Just in case we support const columns serialization.
                    column = column->cloneResized(block.rows());
            }
            else
                column = elem.column->cloneResized(block.rows());
        }
        else
        {
            const auto & col = block.getByName(elem.name);
            if (auto * blob = typeid_cast<ColumnBLOB *>(col.column->assumeMutable().get()))
            {
                blob->addCast(col.type, elem.type);
                column = col.column;
            }
            else
                column = castColumn(col, elem.type);
        }

        res.insert({column, elem.type, elem.name});
    }
    return res;
}

void RemoteQueryExecutor::sendQuery(ClientInfo::QueryKind query_kind, AsyncCallback async_callback)