Method finalize

src/Interpreters/ExpressionActions.cpp:1045–1084

}

void ExpressionActionsChain::finalize()
{
    /// Finalize all steps. Right to left to define unnecessary input columns.
    for (int i = static_cast<int>(steps.size()) - 1; i >= 0; --i)
    {
        auto & required_output = steps[i]->required_output;
        NameSet required_names;
        for (const auto & output : required_output)
            required_names.insert(output.first);

        if (i + 1 < static_cast<int>(steps.size()))
        {
            const NameSet & additional_input = steps[i + 1]->additional_input;
            for (const auto & it : steps[i + 1]->getRequiredColumns())
            {
                if (!additional_input.contains(it.name))
                {
                    auto iter = required_output.find(it.name);
                    if (iter == required_output.end())
                        required_names.insert(it.name);
                    else
                        iter->second = false;
                }
            }
        }
        steps[i]->finalize(required_names);
    }

    /// Adding the ejection of unnecessary columns to the beginning of each step.
    for (size_t i = 1; i < steps.size(); ++i)
    {
        size_t columns_from_previous = steps[i - 1]->getResultColumns().size();

        /// If unnecessary columns are formed at the output of the previous step, we'll add them to the beginning of this step.
        /// Except when we drop all the columns and lose the number of rows in the block.
        if (!steps[i]->getResultColumns().empty()
            && columns_from_previous > steps[i]->getRequiredColumns().size())
            steps[i]->prependProjectInput();
    }
}

ExpressionActionsChainSteps::ExpressionActionsStep * ExpressionActionsChain::getLastExpressionStep(bool allow_empty)
{