ClickHouse/dbms/DataStreams/FilterBlockInputStream.h

#pragma once

#include <DataStreams/IBlockInputStream.h>
#include <Columns/FilterDescription.h>


namespace DB
{

class ExpressionActions;


/** Implements WHERE, HAVING operations.
  * A stream of blocks and an expression, which adds to the block one ColumnUInt8 column containing the filtering conditions, are passed as input.
  * The expression is evaluated and a stream of blocks is returned, which contains only the filtered rows.
  */
class FilterBlockInputStream : public IBlockInputStream
{
private:
    using ExpressionActionsPtr = std::shared_ptr<ExpressionActions>;

public:
    FilterBlockInputStream(const BlockInputStreamPtr & input, ExpressionActionsPtr expression_,
                           String filter_column_name_, bool remove_filter_ = false);

    String getName() const override;
    Block getTotals() override;
    Block getHeader() const override;

protected:
    Block readImpl() override;

    bool remove_filter;

private:
    ExpressionActionsPtr expression;
    Block header;
    String filter_column_name;
    ssize_t filter_column;

    ConstantFilterDescription constant_filter_description;

    Block removeFilterIfNeed(Block && block);
};

}