ClickHouse/dbms/DataStreams/FilterBlockInputStream.cpp

#include <Columns/ColumnsNumber.h>
#include <Columns/ColumnsCommon.h>
#include <Columns/ColumnConst.h>
#include <Columns/FilterDescription.h>
#include <Interpreters/ExpressionActions.h>
#include <Common/typeid_cast.h>

#include <DataStreams/FilterBlockInputStream.h>


namespace DB
{

namespace ErrorCodes
{
}


FilterBlockInputStream::FilterBlockInputStream(const BlockInputStreamPtr & input, ExpressionActionsPtr expression_,
                                               String filter_column_name_, bool remove_filter_)
    : remove_filter(remove_filter_)
    , expression(std::move(expression_))
    , filter_column_name(std::move(filter_column_name_))
{
    children.push_back(input);

    /// Determine position of filter column.
    header = input->getHeader();
    expression->execute(header);

    filter_column = header.getPositionByName(filter_column_name);
    auto & column_elem = header.safeGetByPosition(filter_column);

    /// Isn't the filter already constant?
    if (column_elem.column)
        constant_filter_description = ConstantFilterDescription(*column_elem.column);

    if (!constant_filter_description.always_false
        && !constant_filter_description.always_true)
    {
        /// Replace the filter column to a constant with value 1.
        FilterDescription filter_description_check(*column_elem.column);
        column_elem.column = column_elem.type->createColumnConst(header.rows(), 1u);
    }

    if (remove_filter)
        header.erase(filter_column_name);
}


String FilterBlockInputStream::getName() const { return "Filter"; }


Block FilterBlockInputStream::getTotals()
{
    totals = children.back()->getTotals();
    expression->executeOnTotals(totals);

    return totals;
}


Block FilterBlockInputStream::getHeader() const
{
    return header;
}


Block FilterBlockInputStream::readImpl()
{
    Block res;

    if (constant_filter_description.always_false)
        return removeFilterIfNeed(std::move(res));

    if (expression->checkColumnIsAlwaysFalse(filter_column_name))
        return {};

    /// Until non-empty block after filtering or end of stream.
    while (true)
    {
        res = children.back()->read();
        if (!res)
            return res;

        expression->execute(res);

        if (constant_filter_description.always_true)
            return removeFilterIfNeed(std::move(res));

        size_t columns = res.columns();
        ColumnPtr column = res.safeGetByPosition(filter_column).column;

        /** It happens that at the stage of analysis of expressions (in sample_block) the columns-constants have not been calculated yet,
            *  and now - are calculated. That is, not all cases are covered by the code above.
            * This happens if the function returns a constant for a non-constant argument.
            * For example, `ignore` function.
            */
        constant_filter_description = ConstantFilterDescription(*column);

        if (constant_filter_description.always_false)
        {
            res.clear();
            return res;
        }

        if (constant_filter_description.always_true)
            return removeFilterIfNeed(std::move(res));

        FilterDescription filter_and_holder(*column);

        /** Let's find out how many rows will be in result.
          * To do this, we filter out the first non-constant column
          *  or calculate number of set bytes in the filter.
          */
        size_t first_non_constant_column = 0;
        for (size_t i = 0; i < columns; ++i)
        {
            if (!isColumnConst(*res.safeGetByPosition(i).column))
            {
                first_non_constant_column = i;

                if (first_non_constant_column != static_cast<size_t>(filter_column))
                    break;
            }
        }

        size_t filtered_rows = 0;
        if (first_non_constant_column != static_cast<size_t>(filter_column))
        {
            ColumnWithTypeAndName & current_column = res.safeGetByPosition(first_non_constant_column);
            current_column.column = current_column.column->filter(*filter_and_holder.data, -1);
            filtered_rows = current_column.column->size();
        }
        else
        {
            filtered_rows = countBytesInFilter(*filter_and_holder.data);
        }

        /// If the current block is completely filtered out, let's move on to the next one.
        if (filtered_rows == 0)
            continue;

        /// If all the rows pass through the filter.
        if (filtered_rows == filter_and_holder.data->size())
        {
            /// Replace the column with the filter by a constant.
            res.safeGetByPosition(filter_column).column = res.safeGetByPosition(filter_column).type->createColumnConst(filtered_rows, 1u);
            /// No need to touch the rest of the columns.
            return removeFilterIfNeed(std::move(res));
        }

        /// Filter the rest of the columns.
        for (size_t i = 0; i < columns; ++i)
        {
            ColumnWithTypeAndName & current_column = res.safeGetByPosition(i);

            if (i == static_cast<size_t>(filter_column))
            {
                /// The column with filter itself is replaced with a column with a constant `1`, since after filtering, nothing else will remain.
                /// NOTE User could pass column with something different than 0 and 1 for filter.
                /// Example:
                ///  SELECT materialize(100) AS x WHERE x
                /// will work incorrectly.
                current_column.column = current_column.type->createColumnConst(filtered_rows, 1u);
                continue;
            }

            if (i == first_non_constant_column)
                continue;

            if (isColumnConst(*current_column.column))
                current_column.column = current_column.column->cut(0, filtered_rows);
            else
                current_column.column = current_column.column->filter(*filter_and_holder.data, -1);
        }

        return removeFilterIfNeed(std::move(res));
    }
}


Block FilterBlockInputStream::removeFilterIfNeed(Block && block)
{
    if (block && remove_filter)
        block.erase(static_cast<size_t>(filter_column));

    return std::move(block);
}


}