Method planReadFromStorage

src/QueryPlan/QueryPlanner.cpp:911–1132

}

RelationPlan
QueryPlannerVisitor::planReadFromStorage(IAST & table_ast, ScopePtr table_scope, ASTSelectQuery & origin_query, SqlHints & hints, bool is_table_function)
{
    const auto & storage_analysis = analysis.getStorageAnalysis(table_ast);
    const auto & storage = storage_analysis.storage;
    const auto & alias = table_ast.tryGetAlias();

    auto primary_column_size = table_scope->size();
    const auto & used_columns = analysis.getReadColumns(table_ast);
    const auto & used_sub_columns = analysis.getReadSubColumns(table_ast);
    NamesWithAliases columns_with_aliases;
    // note primary column and sub columns may overlap, we use a map to keep allocated columns
    // e.g. SELECT m{'foo'}, __m__foo from t;
    NameToNameMap columns_to_aliases;
    FieldSymbolInfos field_symbols;

    field_symbols.reserve(primary_column_size);
    columns_with_aliases.reserve(primary_column_size); // may be larger

    assert(used_sub_columns.size() <= primary_column_size);

    for (size_t i = 0; i < primary_column_size; ++i)
    {
        const auto & primary_column_name = table_scope->at(i).getOriginColumnName();
        String primary_column_symbol;
        FieldSymbolInfo::SubColumnToSymbol sub_column_symbols;

        // allocate primary columns, not allocate if it is not used
        if (used_columns.count(i) || (i < used_sub_columns.size() && !used_sub_columns[i].empty()))
        {
            if (!columns_to_aliases.count(primary_column_name))
            {
                primary_column_symbol = context->getSymbolAllocator()->newSymbol(primary_column_name);
                columns_with_aliases.emplace_back(primary_column_name, primary_column_symbol);
                columns_to_aliases.emplace(primary_column_name, primary_column_symbol);
            }
            else
            {
                primary_column_symbol = columns_to_aliases.at(primary_column_name);
            }
        }

        // allocate sub columns
        if (i < used_sub_columns.size())
        {
            for (const auto & sub_column_id : used_sub_columns[i])
            {
                auto sub_column_name = sub_column_id.getSubColumnName(primary_column_name);
                if (!columns_to_aliases.count(sub_column_name))
                {
                    auto sub_column_symbol = context->getSymbolAllocator()->newSymbol(sub_column_name);
                    columns_with_aliases.emplace_back(sub_column_name, sub_column_symbol);
                    columns_to_aliases.emplace(sub_column_name, sub_column_symbol);
                    sub_column_symbols.emplace(sub_column_id, sub_column_symbol);
                }
                else
                {
                    sub_column_symbols.emplace(sub_column_id, columns_to_aliases.at(sub_column_name));