ClickHouse/dbms/include/DB/Functions/FunctionsConversion.h

#pragma once

#include <ext/enumerate.hpp>
#include <ext/collection_cast.hpp>
#include <ext/range.hpp>
#include <type_traits>

#include <DB/IO/WriteBufferFromVector.h>
#include <DB/IO/ReadBufferFromString.h>
#include <DB/IO/Operators.h>
#include <DB/IO/ReadBufferFromMemory.h>
#include <DB/DataTypes/DataTypeFactory.h>
#include <DB/DataTypes/DataTypesNumberFixed.h>
#include <DB/DataTypes/DataTypeString.h>
#include <DB/DataTypes/DataTypeFixedString.h>
#include <DB/DataTypes/DataTypeDate.h>
#include <DB/DataTypes/DataTypeDateTime.h>
#include <DB/DataTypes/DataTypeEnum.h>
#include <DB/DataTypes/DataTypeArray.h>
#include <DB/DataTypes/DataTypeTuple.h>
#include <DB/DataTypes/DataTypeNullable.h>
#include <DB/Columns/ColumnString.h>
#include <DB/Columns/ColumnFixedString.h>
#include <DB/Columns/ColumnConst.h>
#include <DB/Columns/ColumnArray.h>
#include <DB/Columns/ColumnNullable.h>
#include <DB/Core/FieldVisitors.h>
#include <DB/Interpreters/ExpressionActions.h>
#include <DB/Functions/IFunction.h>
#include <DB/Functions/FunctionsMiscellaneous.h>
#include <DB/Functions/FunctionsDateTime.h>


namespace DB
{

namespace ErrorCodes
{
	extern const int ATTEMPT_TO_READ_AFTER_EOF;
	extern const int CANNOT_PARSE_NUMBER;
	extern const int CANNOT_READ_ARRAY_FROM_TEXT;
	extern const int CANNOT_PARSE_INPUT_ASSERTION_FAILED;
	extern const int CANNOT_PARSE_QUOTED_STRING;
	extern const int CANNOT_PARSE_ESCAPE_SEQUENCE;
	extern const int CANNOT_PARSE_DATE;
	extern const int CANNOT_PARSE_DATETIME;
	extern const int CANNOT_PARSE_TEXT;
}


/** Type conversion functions.
  * toType - conversion in "natural way";
  */


/** Conversion of number types to each other, enums to numbers, dates and datetimes to numbers and back: done by straight assignment.
  *  (Date is represented internally as number of days from some day; DateTime - as unix timestamp)
  */
template <typename FromDataType, typename ToDataType, typename Name>
struct ConvertImpl
{
	using FromFieldType = typename FromDataType::FieldType;
	using ToFieldType = typename ToDataType::FieldType;

	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		if (const ColumnVector<FromFieldType> * col_from
			= typeid_cast<const ColumnVector<FromFieldType> *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			auto col_to = std::make_shared<ColumnVector<ToFieldType>>();
			block.safeGetByPosition(result).column = col_to;

			const typename ColumnVector<FromFieldType>::Container_t & vec_from = col_from->getData();
			typename ColumnVector<ToFieldType>::Container_t & vec_to = col_to->getData();
			size_t size = vec_from.size();
			vec_to.resize(size);

			for (size_t i = 0; i < size; ++i)
				vec_to[i] = vec_from[i];
		}
		else if (const ColumnConst<FromFieldType> * col_from
			= typeid_cast<const ColumnConst<FromFieldType> *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			block.safeGetByPosition(result).column = std::make_shared<ColumnConst<ToFieldType>>(col_from->size(), col_from->getData());
		}
		else
			throw Exception("Illegal column " + block.safeGetByPosition(arguments[0]).column->getName()
					+ " of first argument of function " + Name::name,
				ErrorCodes::ILLEGAL_COLUMN);
	}
};


/** Conversion of Date to DateTime: adding 00:00:00 time component.
  */
struct ToDateTimeImpl
{
	static inline UInt32 execute(UInt16 d, const DateLUTImpl & time_zone)
	{
		return time_zone.fromDayNum(DayNum_t(d));
	}
};

template <typename Name> struct ConvertImpl<DataTypeDate, DataTypeDateTime, Name>
	: DateTimeTransformImpl<UInt16, UInt32, ToDateTimeImpl, Name> {};


/// Implementation of toDate function.

template <typename FromType, typename ToType>
struct ToDateTransform32Or64
{
	static inline ToType execute(const FromType & from, const DateLUTImpl & time_zone)
	{
		return (from < 0xFFFF) ? from : time_zone.toDayNum(from);
	}
};

/** Conversion of DateTime to Date: throw off time component.
  */
template <typename Name> struct ConvertImpl<DataTypeDateTime, DataTypeDate, Name>
	: DateTimeTransformImpl<UInt32, UInt16, ToDateImpl, Name> {};

/** Special case of converting (U)Int32 or (U)Int64 (and also, for convenience, Float32, Float64) to Date.
  * If number is less than 65536, then it is treated as DayNum, and if greater or equals, then as unix timestamp.
  * It's a bit illogical, as we actually have two functions in one.
  * But allows to support frequent case,
  *  when user write toDate(UInt32), expecting conversion of unix timestamp to Date.
  *  (otherwise such usage would be frequent mistake).
  */
template <typename Name> struct ConvertImpl<DataTypeUInt32, DataTypeDate, Name>
	: DateTimeTransformImpl<UInt32, UInt16, ToDateTransform32Or64<UInt32, UInt16>, Name> {};
template <typename Name> struct ConvertImpl<DataTypeUInt64, DataTypeDate, Name>
	: DateTimeTransformImpl<UInt64, UInt16, ToDateTransform32Or64<UInt64, UInt16>, Name> {};
template <typename Name> struct ConvertImpl<DataTypeInt32, DataTypeDate, Name>
	: DateTimeTransformImpl<Int32, UInt16, ToDateTransform32Or64<Int32, UInt16>, Name> {};
template <typename Name> struct ConvertImpl<DataTypeInt64, DataTypeDate, Name>
	: DateTimeTransformImpl<Int64, UInt16, ToDateTransform32Or64<Int64, UInt16>, Name> {};
template <typename Name> struct ConvertImpl<DataTypeFloat32, DataTypeDate, Name>
	: DateTimeTransformImpl<Float32, UInt16, ToDateTransform32Or64<Float32, UInt16>, Name> {};
template <typename Name> struct ConvertImpl<DataTypeFloat64, DataTypeDate, Name>
	: DateTimeTransformImpl<Float64, UInt16, ToDateTransform32Or64<Float64, UInt16>, Name> {};


/** Transformation of numbers, dates, datetimes to strings: through formatting.
  */
template <typename DataType>
struct FormatImpl
{
	static void execute(const typename DataType::FieldType x, WriteBuffer & wb, const DataType * type, const DateLUTImpl * time_zone)
	{
		writeText(x, wb);
	}
};

template <>
struct FormatImpl<DataTypeDate>
{
	static void execute(const DataTypeDate::FieldType x, WriteBuffer & wb, const DataTypeDate * type, const DateLUTImpl * time_zone)
	{
		writeDateText(DayNum_t(x), wb);
	}
};

template <>
struct FormatImpl<DataTypeDateTime>
{
	static void execute(const DataTypeDateTime::FieldType x, WriteBuffer & wb, const DataTypeDateTime * type, const DateLUTImpl * time_zone)
	{
		writeDateTimeText(x, wb, *time_zone);
	}
};

template <typename FieldType>
struct FormatImpl<DataTypeEnum<FieldType>>
{
	static void execute(const FieldType x, WriteBuffer & wb, const DataTypeEnum<FieldType> * type, const DateLUTImpl * time_zone)
	{
		writeString(type->getNameForValue(x), wb);
	}
};


/// DataTypeEnum<T> to DataType<T> free conversion
template <typename FieldType, typename Name>
struct ConvertImpl<DataTypeEnum<FieldType>, typename DataTypeFromFieldType<FieldType>::Type, Name>
{
	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		block.safeGetByPosition(result).column = block.safeGetByPosition(arguments[0]).column;
	}
};


/// For functions toDateTime, toUnixTimestamp and toString from DateTime type, second argument with time zone could be specified.
const DateLUTImpl * extractTimeZoneFromFunctionArguments(Block & block, const ColumnNumbers & arguments);


template <typename FromDataType, typename Name>
struct ConvertImpl<FromDataType, DataTypeString, Name>
{
	using FromFieldType = typename FromDataType::FieldType;

	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		const auto & col_with_type_and_name = block.safeGetByPosition(arguments[0]);
		const auto & type = static_cast<const FromDataType &>(*col_with_type_and_name.type);

		const DateLUTImpl * time_zone = nullptr;

		/// For argument of DateTime type, second argument with time zone could be specified.
		if (std::is_same<FromDataType, DataTypeDateTime>::value)
			time_zone = extractTimeZoneFromFunctionArguments(block, arguments);

		if (const auto col_from = typeid_cast<const ColumnVector<FromFieldType> *>(col_with_type_and_name.column.get()))
		{
			auto col_to = std::make_shared<ColumnString>();
			block.safeGetByPosition(result).column = col_to;

			const typename ColumnVector<FromFieldType>::Container_t & vec_from = col_from->getData();
			ColumnString::Chars_t & data_to = col_to->getChars();
			ColumnString::Offsets_t & offsets_to = col_to->getOffsets();
			size_t size = vec_from.size();
			data_to.resize(size * 2);
			offsets_to.resize(size);

			WriteBufferFromVector<ColumnString::Chars_t> write_buffer(data_to);

			for (size_t i = 0; i < size; ++i)
			{
				FormatImpl<FromDataType>::execute(vec_from[i], write_buffer, &type, time_zone);
				writeChar(0, write_buffer);
				offsets_to[i] = write_buffer.count();
			}

			data_to.resize(write_buffer.count());
		}
		else if (const auto col_from = typeid_cast<const ColumnConst<FromFieldType> *>(col_with_type_and_name.column.get()))
		{
			std::vector<char> buf;
			WriteBufferFromVector<std::vector<char> > write_buffer(buf);
			FormatImpl<FromDataType>::execute(col_from->getData(), write_buffer, &type, time_zone);
			block.safeGetByPosition(result).column = std::make_shared<ColumnConstString>(col_from->size(), std::string(&buf[0], write_buffer.count()));
		}
		else
			throw Exception("Illegal column " + block.safeGetByPosition(arguments[0]).column->getName()
					+ " of first argument of function " + Name::name,
				ErrorCodes::ILLEGAL_COLUMN);
	}
};


/// Generic conversion of any type to String.
struct ConvertImplGenericToString
{
	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		const auto & col_with_type_and_name = block.safeGetByPosition(arguments[0]);
		const IDataType & type = *col_with_type_and_name.type;
		const IColumn & col_from = *col_with_type_and_name.column;

		size_t size = col_from.size();

		if (!col_from.isConst())
		{
			auto col_to = std::make_shared<ColumnString>();
			block.safeGetByPosition(result).column = col_to;

			ColumnString::Chars_t & data_to = col_to->getChars();
			ColumnString::Offsets_t & offsets_to = col_to->getOffsets();

			data_to.resize(size * 2);	/// Using coefficient 2 for initial size is arbitary.
			offsets_to.resize(size);

			WriteBufferFromVector<ColumnString::Chars_t> write_buffer(data_to);

			for (size_t i = 0; i < size; ++i)
			{
				type.serializeText(col_from, i, write_buffer);
				writeChar(0, write_buffer);
				offsets_to[i] = write_buffer.count();
			}

			data_to.resize(write_buffer.count());
		}
		else
		{
			String res;

			if (size)
			{
				WriteBufferFromString write_buffer(res);
				type.serializeText(*col_from.cut(0, 1)->convertToFullColumnIfConst(), 0, write_buffer);
			}

			block.safeGetByPosition(result).column = std::make_shared<ColumnConstString>(size, res);
		}
	}
};


/** Conversion of strings to numbers, dates, datetimes: through parsing.
  */
template <typename DataType> void parseImpl(typename DataType::FieldType & x, ReadBuffer & rb, const DateLUTImpl * time_zone)
{
	readText(x, rb);
}

template <> inline void parseImpl<DataTypeDate>(DataTypeDate::FieldType & x, ReadBuffer & rb, const DateLUTImpl * time_zone)
{
	DayNum_t tmp(0);
	readDateText(tmp, rb);
	x = tmp;
}

template <> inline void parseImpl<DataTypeDateTime>(DataTypeDateTime::FieldType & x, ReadBuffer & rb, const DateLUTImpl * time_zone)
{
	time_t tmp = 0;
	readDateTimeText(tmp, rb, *time_zone);
	x = tmp;
}


/** Throw exception with verbose message when string value is not parsed completely.
  */
void throwExceptionForIncompletelyParsedValue(
	ReadBuffer & read_buffer, Block & block, const ColumnNumbers & arguments, size_t result);


template <typename ToDataType, typename Name>
struct ConvertImpl<DataTypeString, ToDataType, Name>
{
	using ToFieldType = typename ToDataType::FieldType;

	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		const DateLUTImpl * time_zone = nullptr;

		/// For conversion to DateTime type, second argument with time zone could be specified.
		if (std::is_same<ToDataType, DataTypeDateTime>::value)
			time_zone = extractTimeZoneFromFunctionArguments(block, arguments);

		if (const ColumnString * col_from = typeid_cast<const ColumnString *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			auto col_to = std::make_shared<ColumnVector<ToFieldType>>();
			block.safeGetByPosition(result).column = col_to;

			typename ColumnVector<ToFieldType>::Container_t & vec_to = col_to->getData();
			size_t size = col_from->size();
			vec_to.resize(size);

			const ColumnString::Chars_t & chars = col_from->getChars();
			const IColumn::Offsets_t & offsets = col_from->getOffsets();

			size_t current_offset = 0;

			for (size_t i = 0; i < size; ++i)
			{
				ReadBufferFromMemory read_buffer(&chars[current_offset], offsets[i] - current_offset - 1);

				parseImpl<ToDataType>(vec_to[i], read_buffer, time_zone);

				if (!read_buffer.eof()
					&& !(std::is_same<ToDataType, DataTypeDate>::value /// Special exception, that allows to parse string with DateTime as Date.
						&& offsets[i] - current_offset - 1 == strlen("YYYY-MM-DD hh:mm:ss")))
					throwExceptionForIncompletelyParsedValue(read_buffer, block, arguments, result);

				current_offset = offsets[i];
			}
		}
		else if (const ColumnConstString * col_from = typeid_cast<const ColumnConstString *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			const String & s = col_from->getData();
			ReadBufferFromString read_buffer(s);
			ToFieldType x = 0;
			parseImpl<ToDataType>(x, read_buffer, time_zone);

			if (!read_buffer.eof()
				&& !(std::is_same<ToDataType, DataTypeDate>::value /// Special exception, that allows to parse string with DateTime as Date.
					&& s.size() == strlen("YYYY-MM-DD hh:mm:ss")))
				throwExceptionForIncompletelyParsedValue(read_buffer, block, arguments, result);

			block.safeGetByPosition(result).column = std::make_shared<ColumnConst<ToFieldType>>(col_from->size(), x);
		}
		else
			throw Exception("Illegal column " + block.safeGetByPosition(arguments[0]).column->getName()
				+ " of first argument of function " + Name::name,
				ErrorCodes::ILLEGAL_COLUMN);
	}
};


template <typename DataType>
typename std::enable_if<std::is_integral<typename DataType::FieldType>::value, bool>::type
tryParseImpl(typename DataType::FieldType & x, ReadBuffer & rb)
{
	return tryReadIntText(x, rb);
}

template <typename DataType>
typename std::enable_if<std::is_floating_point<typename DataType::FieldType>::value, bool>::type
tryParseImpl(typename DataType::FieldType & x, ReadBuffer & rb)
{
	return tryReadFloatText(x, rb);
}


/** Conversion from String through parsing, which returns default value instead of throwing an exception.
  */
template <typename ToDataType, typename Name>
struct ConvertOrZeroImpl
{
	using ToFieldType = typename ToDataType::FieldType;

	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		if (const ColumnString * col_from = typeid_cast<const ColumnString *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			auto col_to = std::make_shared<ColumnVector<ToFieldType>>();
			block.safeGetByPosition(result).column = col_to;

			typename ColumnVector<ToFieldType>::Container_t & vec_to = col_to->getData();
			size_t size = col_from->size();
			vec_to.resize(size);

			const ColumnString::Chars_t & chars = col_from->getChars();
			const IColumn::Offsets_t & offsets = col_from->getOffsets();

			size_t current_offset = 0;

			for (size_t i = 0; i < size; ++i)
			{
				ReadBufferFromMemory read_buffer(&chars[current_offset], offsets[i] - current_offset - 1);

				/// NOTE Need to implement for Date and DateTime too.
				if (!tryParseImpl<ToDataType>(vec_to[i], read_buffer) || !read_buffer.eof())
					vec_to[i] = 0;

				current_offset = offsets[i];
			}
		}
		else if (const ColumnConstString * col_from = typeid_cast<const ColumnConstString *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			const String & s = col_from->getData();
			ReadBufferFromString read_buffer(s);
			ToFieldType x = 0;
			if (!tryParseImpl<ToDataType>(x, read_buffer) || !read_buffer.eof())
				x = 0;
			block.safeGetByPosition(result).column = std::make_shared<ColumnConst<ToFieldType>>(col_from->size(), x);
		}
		else
			throw Exception("Illegal column " + block.safeGetByPosition(arguments[0]).column->getName()
					+ " of first argument of function " + Name::name,
				ErrorCodes::ILLEGAL_COLUMN);
	}
};


/// Generic conversion of any type from String. Used for complex types: Array and Tuple.
struct ConvertImplGenericFromString
{
	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		const IColumn & col_from = *block.safeGetByPosition(arguments[0]).column;
		size_t size = col_from.size();

		ColumnWithTypeAndName & column_type_name_to = block.safeGetByPosition(result);
		const IDataType & data_type_to = *column_type_name_to.type;

		if (const ColumnString * col_from_string = typeid_cast<const ColumnString *>(&col_from))
		{
			column_type_name_to.column = data_type_to.createColumn();

			if (!size)
				return;

			IColumn & column_to = *column_type_name_to.column;
			column_to.reserve(size);

			const ColumnString::Chars_t & chars = col_from_string->getChars();
			const IColumn::Offsets_t & offsets = col_from_string->getOffsets();

			size_t current_offset = 0;

			for (size_t i = 0; i < size; ++i)
			{
				ReadBufferFromMemory read_buffer(&chars[current_offset], offsets[i] - current_offset - 1);

				data_type_to.deserializeTextEscaped(column_to, read_buffer);

				if (!read_buffer.eof())
					throwExceptionForIncompletelyParsedValue(read_buffer, block, arguments, result);

				current_offset = offsets[i];
			}
		}
		else if (const ColumnConstString * col_from_const_string = typeid_cast<const ColumnConstString *>(&col_from))
		{
			const String & s = col_from_const_string->getData();
			ReadBufferFromString read_buffer(s);

			auto tmp_col = data_type_to.createColumn();
			data_type_to.deserializeTextEscaped(*tmp_col, read_buffer);

			if (!read_buffer.eof())
				throwExceptionForIncompletelyParsedValue(read_buffer, block, arguments, result);

			block.safeGetByPosition(result).column = data_type_to.createConstColumn(size, (*tmp_col)[0]);
		}
		else
			throw Exception("Illegal column " + block.safeGetByPosition(arguments[0]).column->getName()
					+ " of first argument of conversion function from string",
				ErrorCodes::ILLEGAL_COLUMN);
	}
};


/// Function toUnixTimestamp has exactly the same implementation as toDateTime of String type.
/// Note that time zone argument could be passed only for toUnixTimestamp function.
struct NameToUnixTimestamp	{ static constexpr auto name = "toUnixTimestamp"; };

template <>
struct ConvertImpl<DataTypeString, DataTypeUInt32, NameToUnixTimestamp>
	: ConvertImpl<DataTypeString, DataTypeDateTime, NameToUnixTimestamp> {};


/** If types are identical, just take reference to column.
  */
template <typename Name>
struct ConvertImpl<DataTypeString, DataTypeString, Name>
{
	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		block.safeGetByPosition(result).column = block.safeGetByPosition(arguments[0]).column;
	}
};


/** Conversion from FixedString through parsing.
  */
template <typename ToDataType, typename Name>
struct ConvertImpl<DataTypeFixedString, ToDataType, Name>
{
	using ToFieldType = typename ToDataType::FieldType;

	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		if (const ColumnFixedString * col_from = typeid_cast<const ColumnFixedString *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			const DateLUTImpl * time_zone = nullptr;

			/// For conversion to DateTime type, second argument with time zone could be specified.
			if (std::is_same<ToDataType, DataTypeDateTime>::value)
				time_zone = extractTimeZoneFromFunctionArguments(block, arguments);

			auto col_to = std::make_shared<ColumnVector<ToFieldType>>();
			block.safeGetByPosition(result).column = col_to;

			const ColumnFixedString::Chars_t & data_from = col_from->getChars();
			size_t n = col_from->getN();
			typename ColumnVector<ToFieldType>::Container_t & vec_to = col_to->getData();
			size_t size = col_from->size();
			vec_to.resize(size);

			for (size_t i = 0; i < size; ++i)
			{
				ReadBufferFromMemory read_buffer(&data_from[i * n], n);
				const char * end = read_buffer.buffer().end();
				parseImpl<ToDataType>(vec_to[i], read_buffer, time_zone);

				if (!read_buffer.eof())
				{
					while (read_buffer.position() < end && *read_buffer.position() == 0)
						++read_buffer.position();

					if (read_buffer.position() < end)
						throwExceptionForIncompletelyParsedValue(read_buffer, block, arguments, result);
				}
			}
		}
		else if (typeid_cast<const ColumnConstString *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			ConvertImpl<DataTypeString, ToDataType, Name>::execute(block, arguments, result);
		}
		else
			throw Exception("Illegal column " + block.safeGetByPosition(arguments[0]).column->getName()
					+ " of first argument of function " + Name::name,
				ErrorCodes::ILLEGAL_COLUMN);
	}
};


/** Conversion from FixedString to String.
  * Cutting sequences of zero bytes from end of strings.
  */
template <typename Name>
struct ConvertImpl<DataTypeFixedString, DataTypeString, Name>
{
	static void execute(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		if (const ColumnFixedString * col_from = typeid_cast<const ColumnFixedString *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			auto col_to = std::make_shared<ColumnString>();
			block.safeGetByPosition(result).column = col_to;

			const ColumnFixedString::Chars_t & data_from = col_from->getChars();
			ColumnString::Chars_t & data_to = col_to->getChars();
			ColumnString::Offsets_t & offsets_to = col_to->getOffsets();
			size_t size = col_from->size();
			size_t n = col_from->getN();
			data_to.resize(size * (n + 1));		/// + 1 - zero terminator
			offsets_to.resize(size);

			size_t offset_from = 0;
			size_t offset_to = 0;
			for (size_t i = 0; i < size; ++i)
			{
				size_t bytes_to_copy = n;
				while (bytes_to_copy > 0 && data_from[offset_from + bytes_to_copy - 1] == 0)
					--bytes_to_copy;

				memcpy(&data_to[offset_to], &data_from[offset_from], bytes_to_copy);
				offset_from += n;
				offset_to += bytes_to_copy;
				data_to[offset_to] = 0;
				++offset_to;
				offsets_to[i] = offset_to;
			}

			data_to.resize(offset_to);
		}
		else if (const ColumnConstString * col_from = typeid_cast<const ColumnConstString *>(block.safeGetByPosition(arguments[0]).column.get()))
		{
			const String & s = col_from->getData();

			size_t bytes_to_copy = s.size();
			while (bytes_to_copy > 0 && s[bytes_to_copy - 1] == 0)
				--bytes_to_copy;

			block.safeGetByPosition(result).column = std::make_shared<ColumnConstString>(col_from->size(), s.substr(0, bytes_to_copy));
		}
		else
			throw Exception("Illegal column " + block.safeGetByPosition(arguments[0]).column->getName()
					+ " of first argument of function " + Name::name,
				ErrorCodes::ILLEGAL_COLUMN);
	}
};


/// Declared early because used below.
struct NameToDate			{ static constexpr auto name = "toDate"; };
struct NameToString			{ static constexpr auto name = "toString"; };


template <typename ToDataType, typename Name, typename MonotonicityImpl>
class FunctionConvert : public IFunction
{
public:
	using Monotonic = MonotonicityImpl;

	static constexpr auto name = Name::name;
	static FunctionPtr create(const Context & context) { return std::make_shared<FunctionConvert>(); }

	String getName() const override
	{
		return name;
	}

	bool isVariadic() const override { return true; }
	size_t getNumberOfArguments() const override { return 0; }
	bool isInjective(const Block &) override { return std::is_same<Name, NameToString>::value; }

	/// Получить тип результата по типам аргументов. Если функция неприменима для данных аргументов - кинуть исключение.
	DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
	{
		return getReturnTypeInternal(arguments);
	}

	void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result) override
	{
		try
		{
			executeInternal(block, arguments, result);
		}
		catch (Exception & e)
		{
			/// More convenient error message.
			if (e.code() == ErrorCodes::ATTEMPT_TO_READ_AFTER_EOF)
			{
				e.addMessage("Cannot parse "
					+ block.getByPosition(result).type->getName() + " from "
					+ block.getByPosition(arguments[0]).type->getName()
					+ ", because value is too short");
			}
			else if (e.code() == ErrorCodes::CANNOT_PARSE_NUMBER
				|| e.code() == ErrorCodes::CANNOT_READ_ARRAY_FROM_TEXT
				|| e.code() == ErrorCodes::CANNOT_PARSE_INPUT_ASSERTION_FAILED
				|| e.code() == ErrorCodes::CANNOT_PARSE_QUOTED_STRING
				|| e.code() == ErrorCodes::CANNOT_PARSE_ESCAPE_SEQUENCE
				|| e.code() == ErrorCodes::CANNOT_PARSE_DATE
				|| e.code() == ErrorCodes::CANNOT_PARSE_DATETIME)
			{
				e.addMessage("Cannot parse "
					+ block.getByPosition(result).type->getName() + " from "
					+ block.getByPosition(arguments[0]).type->getName());
			}

			throw;
		}
	}

	bool hasInformationAboutMonotonicity() const override
	{
		return Monotonic::has();
	}

	Monotonicity getMonotonicityForRange(const IDataType & type, const Field & left, const Field & right) const override
	{
		return Monotonic::get(type, left, right);
	}

private:
	void executeInternal(Block & block, const ColumnNumbers & arguments, size_t result)
	{
		IDataType * from_type = block.safeGetByPosition(arguments[0]).type.get();

		if      (typeid_cast<const DataTypeUInt8 *		>(from_type)) ConvertImpl<DataTypeUInt8, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeUInt16 *		>(from_type)) ConvertImpl<DataTypeUInt16, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeUInt32 *		>(from_type)) ConvertImpl<DataTypeUInt32, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeUInt64 *		>(from_type)) ConvertImpl<DataTypeUInt64, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeInt8 *		>(from_type)) ConvertImpl<DataTypeInt8, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeInt16 *		>(from_type)) ConvertImpl<DataTypeInt16, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeInt32 *		>(from_type)) ConvertImpl<DataTypeInt32, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeInt64 *		>(from_type)) ConvertImpl<DataTypeInt64, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeFloat32 *	>(from_type)) ConvertImpl<DataTypeFloat32, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeFloat64 *	>(from_type)) ConvertImpl<DataTypeFloat64, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeDate *		>(from_type)) ConvertImpl<DataTypeDate, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeDateTime *	>(from_type)) ConvertImpl<DataTypeDateTime,	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeString *		>(from_type)) ConvertImpl<DataTypeString, 	ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeFixedString *>(from_type)) ConvertImpl<DataTypeFixedString, ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeEnum8 *>(from_type))		  ConvertImpl<DataTypeEnum8, ToDataType, Name>::execute(block, arguments, result);
		else if (typeid_cast<const DataTypeEnum16 *>(from_type))	  ConvertImpl<DataTypeEnum16, ToDataType, Name>::execute(block, arguments, result);
		else
		{
			/// Generic conversion of any type to String.
			if (std::is_same<ToDataType, DataTypeString>::value)
			{
				ConvertImplGenericToString::execute(block, arguments, result);
			}
			else
				throw Exception("Illegal type " + block.safeGetByPosition(arguments[0]).type->getName() + " of argument of function " + getName(),
					ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
		}
	}

	template<typename ToDataType2 = ToDataType, typename Name2 = Name>
	DataTypePtr getReturnTypeInternal(const DataTypes & arguments,
		typename std::enable_if<!(std::is_same<ToDataType2, DataTypeString>::value ||
			std::is_same<Name2, NameToUnixTimestamp>::value ||
			std::is_same<Name2, NameToDate>::value)>::type * = nullptr) const
	{
		if (arguments.size() != 1)
			throw Exception("Number of arguments for function " + getName() + " doesn't match: passed "
				+ toString(arguments.size()) + ", should be 1.",
				ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

		return std::make_shared<ToDataType>();
	}

	/** Conversion of anything to String. For DateTime, it allows second optional argument - time zone.
	  */
	template<typename ToDataType2 = ToDataType, typename Name2 = Name>
	DataTypePtr getReturnTypeInternal(const DataTypes & arguments,
		typename std::enable_if<std::is_same<ToDataType2, DataTypeString>::value>::type * = nullptr) const
	{
		if ((arguments.size() < 1) || (arguments.size() > 2))
			throw Exception("Number of arguments for function " + getName() + " doesn't match: passed "
				+ toString(arguments.size()) + ", should be 1 or 2.",
				ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

		if (typeid_cast<const DataTypeDateTime *>(arguments[0].get()) == nullptr)
		{
			if (arguments.size() != 1)
				throw Exception("Number of arguments for function " + getName() + " doesn't match: passed "
					+ toString(arguments.size()) + ", should be 1.",
					ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
		}
		else if ((arguments.size() == 2) && (typeid_cast<const DataTypeString *>(arguments[1].get()) == nullptr))
		{
			throw Exception{
				"Illegal type " + arguments[1]->getName() + " of argument of function " + getName(),
				ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT
			};
		}

		return std::make_shared<ToDataType2>();
	}

	template<typename ToDataType2 = ToDataType, typename Name2 = Name>
	DataTypePtr getReturnTypeInternal(const DataTypes & arguments,
		typename std::enable_if<std::is_same<Name2, NameToUnixTimestamp>::value, void>::type * = nullptr) const
	{
		if ((arguments.size() < 1) || (arguments.size() > 2))
			throw Exception("Number of arguments for function " + getName() + " doesn't match: passed "
				+ toString(arguments.size()) + ", should be 1 or 2.",
				ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

		if (typeid_cast<const DataTypeString *>(arguments[0].get()) == nullptr)
		{
			if (arguments.size() != 1)
				throw Exception("Number of arguments for function " + getName() + " doesn't match: passed "
					+ toString(arguments.size()) + ", should be 1.",
					ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
		}
		else if ((arguments.size() == 2) && (typeid_cast<const DataTypeString *>(arguments[1].get()) == nullptr))
		{
			throw Exception{
				"Illegal type " + arguments[1]->getName() + " of argument of function " + getName(),
				ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT
			};
		}

		return std::make_shared<ToDataType2>();
	}

	template<typename ToDataType2 = ToDataType, typename Name2 = Name>
	DataTypePtr getReturnTypeInternal(const DataTypes & arguments,
		typename std::enable_if<std::is_same<Name2, NameToDate>::value>::type * = nullptr) const
	{
		if ((arguments.size() < 1) || (arguments.size() > 2))
			throw Exception("Number of arguments for function " + getName() + " doesn't match: passed "
				+ toString(arguments.size()) + ", should be 1 or 2.",
				ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);

		if ((arguments.size() == 2) && (typeid_cast<const DataTypeString *>(arguments[1].get()) == nullptr))
		{
			throw Exception{
				"Illegal type " + arguments[1]->getName() + " of 2nd argument of function " + getName(),
				ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT
			};
		}

		return std::make_shared<ToDataType2>();
	}
};


/** Functions tryToT (where T is number of date or datetime type):
  *  try to convert from String to type T through parsing,
  *  if cannot parse, return default value instead of throwing exception.
  * NOTE Also need implement tryToUnixTimestamp with timezone.
  */
template <typename ToDataType, typename Name>
class FunctionConvertOrZero : public IFunction
{
public:
	static constexpr auto name = Name::name;
	static FunctionPtr create(const Context & context) { return std::make_shared<FunctionConvertOrZero>(); }

	String getName() const override
	{
		return name;
	}

	size_t getNumberOfArguments() const override { return 1; }

	DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
	{
		return std::make_shared<ToDataType>();
	}

	void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result) override
	{
		IDataType * from_type = block.safeGetByPosition(arguments[0]).type.get();

		if (typeid_cast<const DataTypeString *>(from_type))
			ConvertOrZeroImpl<ToDataType, Name>::execute(block, arguments, result);
		else
			throw Exception("Illegal type " + block.safeGetByPosition(arguments[0]).type->getName() + " of argument of function " + getName()
				+ ". Only String argument is accepted for try-conversion function. For other arguments, use function without 'try'.",
				ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
	}
};


/** Conversion to fixed string is implemented only for strings.
  */
class FunctionToFixedString : public IFunction
{
public:
	static constexpr auto name = "toFixedString";
	static FunctionPtr create(const Context & context) { return std::make_shared<FunctionToFixedString>(); };

	/// Получить имя функции.
	String getName() const override
	{
		return name;
	}

	size_t getNumberOfArguments() const override { return 2; }
	bool isInjective(const Block &) override { return true; }

	/** Получить тип результата по типам аргументов и значениям константных аргументов.
	  * Если функция неприменима для данных аргументов - кинуть исключение.
	  * Для неконстантных столбцов arguments[i].column = nullptr.
	  */
	void getReturnTypeAndPrerequisitesImpl(const ColumnsWithTypeAndName & arguments,
		DataTypePtr & out_return_type,
		std::vector<ExpressionAction> & out_prerequisites) override
	{
		if (!arguments[1].column)
			throw Exception("Second argument for function " + getName() + " must be constant", ErrorCodes::ILLEGAL_COLUMN);
		if (!typeid_cast<const DataTypeString *>(arguments[0].type.get()) &&
			!typeid_cast<const DataTypeFixedString *>(arguments[0].type.get()))
			throw Exception(getName() + " is only implemented for types String and FixedString", ErrorCodes::NOT_IMPLEMENTED);

		const size_t n = getSize(arguments[1]);

		out_return_type = std::make_shared<DataTypeFixedString>(n);
	}

	/// Выполнить функцию над блоком.
	void executeImpl(Block & block, const ColumnNumbers & arguments, const size_t result) override
	{
		const auto n = getSize(block.safeGetByPosition(arguments[1]));
		return execute(block, arguments, result, n);
	}

	static void execute(Block & block, const ColumnNumbers & arguments, const size_t result, const size_t n)
	{
		const auto & column = block.safeGetByPosition(arguments[0]).column;

		if (const auto column_const = typeid_cast<const ColumnConstString *>(column.get()))
		{
			if (column_const->getData().size() > n)
				throw Exception("String too long for type FixedString(" + toString(n) + ")",
					ErrorCodes::TOO_LARGE_STRING_SIZE);

			auto resized_string = column_const->getData();
			resized_string.resize(n);

			block.safeGetByPosition(result).column = std::make_shared<ColumnConst<String>>(
				column_const->size(), std::move(resized_string), std::make_shared<DataTypeFixedString>(n));
		}
		else if (const auto column_string = typeid_cast<const ColumnString *>(column.get()))
		{
			const auto column_fixed = std::make_shared<ColumnFixedString>(n);
			ColumnPtr result_ptr = column_fixed;

			auto & out_chars = column_fixed->getChars();
			const auto & in_chars = column_string->getChars();
			const auto & in_offsets = column_string->getOffsets();

			out_chars.resize_fill(in_offsets.size() * n);

			for (size_t i = 0; i < in_offsets.size(); ++i)
			{
				const size_t off = i ? in_offsets[i - 1] : 0;
				const size_t len = in_offsets[i] - off - 1;
				if (len > n)
					throw Exception("String too long for type FixedString(" + toString(n) + ")",
						ErrorCodes::TOO_LARGE_STRING_SIZE);
				memcpy(&out_chars[i * n], &in_chars[off], len);
			}

			block.safeGetByPosition(result).column = result_ptr;
		}
		else if (const auto column_fixed_string = typeid_cast<const ColumnFixedString *>(column.get()))
		{
			const auto src_n = column_fixed_string->getN();
			if (src_n > n)
				throw Exception{
					"String too long for type FixedString(" + toString(n) + ")",
					ErrorCodes::TOO_LARGE_STRING_SIZE
				};

			const auto column_fixed = std::make_shared<ColumnFixedString>(n);
			block.safeGetByPosition(result).column = column_fixed;

			auto & out_chars = column_fixed->getChars();
			const auto & in_chars = column_fixed_string->getChars();
			const auto size = column_fixed_string->size();
			out_chars.resize_fill(size * n);

			for (const auto i : ext::range(0, size))
				memcpy(&out_chars[i * n], &in_chars[i * src_n], src_n);
		}
		else
			throw Exception("Unexpected column: " + column->getName(), ErrorCodes::ILLEGAL_COLUMN);
	}

private:
	template <typename T>
	bool getSizeTyped(const ColumnWithTypeAndName & column, size_t & out_size)
	{
		if (!typeid_cast<const typename DataTypeFromFieldType<T>::Type *>(column.type.get()))
			return false;
		const ColumnConst<T> * column_const = typeid_cast<const ColumnConst<T> *>(column.column.get());
		if (!column_const)
			throw Exception("Unexpected type of column for FixedString length: " + column.column->getName(), ErrorCodes::ILLEGAL_COLUMN);
		T s = column_const->getData();
		if (s <= 0)
			throw Exception("FixedString length must be positive (unlike " + toString(s) + ")", ErrorCodes::ILLEGAL_COLUMN);
		out_size = static_cast<size_t>(s);
		return true;
	}

	size_t getSize(const ColumnWithTypeAndName & column)
	{
		size_t res;
		if (getSizeTyped<UInt8>(column, res) ||
			getSizeTyped<UInt16>(column, res) ||
			getSizeTyped<UInt32>(column, res) ||
			getSizeTyped<UInt64>(column, res) ||
			getSizeTyped< Int8 >(column, res) ||
			getSizeTyped< Int16>(column, res) ||
			getSizeTyped< Int32>(column, res) ||
			getSizeTyped< Int64>(column, res))
			return res;
		throw Exception("Length of FixedString must be integer; got " + column.type->getName(), ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);
	}
};


/// Monotonicity.

struct PositiveMonotonicity
{
	static bool has() { return true; }
	static IFunction::Monotonicity get(const IDataType & type, const Field & left, const Field & right)
	{
		return { true };
	}
};

template <typename T>
struct ToIntMonotonicity
{
	static bool has() { return true; }

	template <typename T2 = T>
	static UInt64 divideByRangeOfType(typename std::enable_if_t<sizeof(T2) != sizeof(UInt64), UInt64> x) { return x >> (sizeof(T) * 8); };

	template <typename T2 = T>
	static UInt64 divideByRangeOfType(typename std::enable_if_t<sizeof(T2) == sizeof(UInt64), UInt64> x) { return 0; };

	static IFunction::Monotonicity get(const IDataType & type, const Field & left, const Field & right)
	{
		size_t size_of_type = type.getSizeOfField();

		/// If type is expanding, then function is monotonic.
		if (sizeof(T) > size_of_type)
			return { true };

		/// If type is same, too. (Enum has separate case, because it is different data type)
		if (typeid_cast<const typename DataTypeFromFieldType<T>::Type *>(&type) ||
			typeid_cast<const DataTypeEnum<T> *>(&type))
			return { true };

		/// In other cases, if range is unbounded, we don't know, whether function is monotonic or not.
		if (left.isNull() || right.isNull())
			return {};

		/// If converting from float, for monotonicity, arguments must fit in range of result type.
		if (typeid_cast<const DataTypeFloat32 *>(&type)
			|| typeid_cast<const DataTypeFloat64 *>(&type))
		{
			Float64 left_float = left.get<Float64>();
			Float64 right_float = right.get<Float64>();

			if (left_float >= std::numeric_limits<T>::min() && left_float <= std::numeric_limits<T>::max()
				&& right_float >= std::numeric_limits<T>::min() && right_float <= std::numeric_limits<T>::max())
				return { true };

			return {};
		}

		/// If signedness of type is changing, or converting from Date, DateTime, then arguments must be from same half,
		///  and after conversion, resulting values must be from same half.
		/// Just in case, it is required in rest of cases too.
		if ((left.get<Int64>() >= 0) != (right.get<Int64>() >= 0)
			|| (T(left.get<Int64>()) >= 0) != (T(right.get<Int64>()) >= 0))
			return {};

		/// If type is shrinked, then for monotonicity, all bits other than that fits, must be same.
		if (divideByRangeOfType(left.get<UInt64>()) != divideByRangeOfType(right.get<UInt64>()))
			return {};

		return { true };
	}
};

/** Монотонность для функции toString определяем, в основном, для тестовых целей.
  * Всерьёз вряд ли кто-нибудь рассчитывает на оптимизацию запросов с условиями toString(CounterID) = 34.
  */
struct ToStringMonotonicity
{
	static bool has() { return true; }

	static IFunction::Monotonicity get(const IDataType & type, const Field & left, const Field & right)
	{
		IFunction::Monotonicity positive(true, true);
		IFunction::Monotonicity not_monotonic;

		/// Функция toString монотонна, если аргумент - Date или DateTime, или неотрицательные числа с одинаковым количеством знаков.

		if (typeid_cast<const DataTypeDate *>(&type)
			|| typeid_cast<const DataTypeDateTime *>(&type))
			return positive;

		if (left.isNull() || right.isNull())
			return {};

		if (left.getType() == Field::Types::UInt64
			&& right.getType() == Field::Types::UInt64)
		{
			return (left.get<Int64>() == 0 && right.get<Int64>() == 0)
				|| (floor(log10(left.get<UInt64>())) == floor(log10(right.get<UInt64>())))
				? positive : not_monotonic;
		}

		if (left.getType() == Field::Types::Int64
			&& right.getType() == Field::Types::Int64)
		{
			return (left.get<Int64>() == 0 && right.get<Int64>() == 0)
				|| (left.get<Int64>() > 0 && right.get<Int64>() > 0 && floor(log10(left.get<Int64>())) == floor(log10(right.get<Int64>())))
				? positive : not_monotonic;
		}

		return not_monotonic;
	}
};


struct NameToUInt8 			{ static constexpr auto name = "toUInt8"; };
struct NameToUInt16 		{ static constexpr auto name = "toUInt16"; };
struct NameToUInt32 		{ static constexpr auto name = "toUInt32"; };
struct NameToUInt64 		{ static constexpr auto name = "toUInt64"; };
struct NameToInt8 			{ static constexpr auto name = "toInt8"; };
struct NameToInt16	 		{ static constexpr auto name = "toInt16"; };
struct NameToInt32			{ static constexpr auto name = "toInt32"; };
struct NameToInt64			{ static constexpr auto name = "toInt64"; };
struct NameToFloat32		{ static constexpr auto name = "toFloat32"; };
struct NameToFloat64		{ static constexpr auto name = "toFloat64"; };
struct NameToDateTime		{ static constexpr auto name = "toDateTime"; };

using FunctionToUInt8 		= FunctionConvert<DataTypeUInt8,	NameToUInt8,	ToIntMonotonicity<UInt8>>;
using FunctionToUInt16 		= FunctionConvert<DataTypeUInt16,	NameToUInt16,	ToIntMonotonicity<UInt16>>;
using FunctionToUInt32 		= FunctionConvert<DataTypeUInt32,	NameToUInt32,	ToIntMonotonicity<UInt32>>;
using FunctionToUInt64 		= FunctionConvert<DataTypeUInt64,	NameToUInt64,	ToIntMonotonicity<UInt64>>;
using FunctionToInt8 		= FunctionConvert<DataTypeInt8,		NameToInt8,		ToIntMonotonicity<Int8>>;
using FunctionToInt16 		= FunctionConvert<DataTypeInt16,	NameToInt16,	ToIntMonotonicity<Int16>>;
using FunctionToInt32 		= FunctionConvert<DataTypeInt32,	NameToInt32,	ToIntMonotonicity<Int32>>;
using FunctionToInt64 		= FunctionConvert<DataTypeInt64,	NameToInt64,	ToIntMonotonicity<Int64>>;
using FunctionToFloat32 	= FunctionConvert<DataTypeFloat32,	NameToFloat32,	PositiveMonotonicity>;
using FunctionToFloat64 	= FunctionConvert<DataTypeFloat64,	NameToFloat64,	PositiveMonotonicity>;
using FunctionToDate 		= FunctionConvert<DataTypeDate,		NameToDate,		ToIntMonotonicity<UInt16>>;
using FunctionToDateTime 	= FunctionConvert<DataTypeDateTime,	NameToDateTime,	ToIntMonotonicity<UInt32>>;
using FunctionToString 		= FunctionConvert<DataTypeString,	NameToString, 	ToStringMonotonicity>;
using FunctionToUnixTimestamp = FunctionConvert<DataTypeUInt32,	NameToUnixTimestamp, ToIntMonotonicity<UInt32>>;

template <typename DataType> struct FunctionTo;
template <> struct FunctionTo<DataTypeUInt8> { using Type = FunctionToUInt8; };
template <> struct FunctionTo<DataTypeUInt16> { using Type = FunctionToUInt16; };
template <> struct FunctionTo<DataTypeUInt32> { using Type = FunctionToUInt32; };
template <> struct FunctionTo<DataTypeUInt64> { using Type = FunctionToUInt64; };
template <> struct FunctionTo<DataTypeInt8> { using Type = FunctionToInt8; };
template <> struct FunctionTo<DataTypeInt16> { using Type = FunctionToInt16; };
template <> struct FunctionTo<DataTypeInt32> { using Type = FunctionToInt32; };
template <> struct FunctionTo<DataTypeInt64> { using Type = FunctionToInt64; };
template <> struct FunctionTo<DataTypeFloat32> { using Type = FunctionToFloat32; };
template <> struct FunctionTo<DataTypeFloat64> { using Type = FunctionToFloat64; };
template <> struct FunctionTo<DataTypeDate> { using Type = FunctionToDate; };
template <> struct FunctionTo<DataTypeDateTime> { using Type = FunctionToDateTime; };
template <> struct FunctionTo<DataTypeString> { using Type = FunctionToString; };
template <> struct FunctionTo<DataTypeFixedString> { using Type = FunctionToFixedString; };
template <typename FieldType> struct FunctionTo<DataTypeEnum<FieldType>>
	: FunctionTo<typename DataTypeFromFieldType<FieldType>::Type>
{
};

struct NameToUInt8OrZero 		{ static constexpr auto name = "toUInt8OrZero"; };
struct NameToUInt16OrZero 		{ static constexpr auto name = "toUInt16OrZero"; };
struct NameToUInt32OrZero 		{ static constexpr auto name = "toUInt32OrZero"; };
struct NameToUInt64OrZero 		{ static constexpr auto name = "toUInt64OrZero"; };
struct NameToInt8OrZero 		{ static constexpr auto name = "toInt8OrZero"; };
struct NameToInt16OrZero	 	{ static constexpr auto name = "toInt16OrZero"; };
struct NameToInt32OrZero		{ static constexpr auto name = "toInt32OrZero"; };
struct NameToInt64OrZero		{ static constexpr auto name = "toInt64OrZero"; };
struct NameToFloat32OrZero		{ static constexpr auto name = "toFloat32OrZero"; };
struct NameToFloat64OrZero		{ static constexpr auto name = "toFloat64OrZero"; };

using FunctionToUInt8OrZero 	= FunctionConvertOrZero<DataTypeUInt8,		NameToUInt8OrZero>;
using FunctionToUInt16OrZero 	= FunctionConvertOrZero<DataTypeUInt16,		NameToUInt16OrZero>;
using FunctionToUInt32OrZero 	= FunctionConvertOrZero<DataTypeUInt32,		NameToUInt32OrZero>;
using FunctionToUInt64OrZero 	= FunctionConvertOrZero<DataTypeUInt64,		NameToUInt64OrZero>;
using FunctionToInt8OrZero 		= FunctionConvertOrZero<DataTypeInt8,		NameToInt8OrZero>;
using FunctionToInt16OrZero 	= FunctionConvertOrZero<DataTypeInt16,		NameToInt16OrZero>;
using FunctionToInt32OrZero 	= FunctionConvertOrZero<DataTypeInt32,		NameToInt32OrZero>;
using FunctionToInt64OrZero 	= FunctionConvertOrZero<DataTypeInt64,		NameToInt64OrZero>;
using FunctionToFloat32OrZero 	= FunctionConvertOrZero<DataTypeFloat32,	NameToFloat32OrZero>;
using FunctionToFloat64OrZero 	= FunctionConvertOrZero<DataTypeFloat64,	NameToFloat64OrZero>;


class FunctionCast final : public IFunction
{
	using WrapperType = std::function<void(Block &, const ColumnNumbers &, size_t)>;
	const Context & context;
	WrapperType wrapper_function;
	std::function<Monotonicity(const IDataType &, const Field &, const Field &)> monotonicity_for_range;

public:
	FunctionCast(const Context & context) : context(context) {}
private:

	template <typename DataType>
	WrapperType createWrapper(const DataTypePtr & from_type, const DataType * const)
	{
		using FunctionType = typename FunctionTo<DataType>::Type;

		auto function = FunctionType::create(context);

		/// Check conversion using underlying function
		(void) function->getReturnType({ from_type });

		return [function] (Block & block, const ColumnNumbers & arguments, const size_t result) {
			function->execute(block, arguments, result);
		};
	}

	static WrapperType createFixedStringWrapper(const DataTypePtr & from_type, const size_t N)
	{
		if (!typeid_cast<const DataTypeString *>(from_type.get()) &&
			!typeid_cast<const DataTypeFixedString *>(from_type.get()))
			throw Exception{
				"CAST AS FixedString is only implemented for types String and FixedString",
				ErrorCodes::NOT_IMPLEMENTED
			};

		return [N] (Block & block, const ColumnNumbers & arguments, const size_t result)
		{
			FunctionToFixedString::execute(block, arguments, result, N);
		};
	}

	WrapperType createArrayWrapper(const DataTypePtr & from_type_untyped, const DataTypeArray * to_type)
	{
		/// Conversion from String through parsing.
		if (typeid_cast<const DataTypeString *>(from_type_untyped.get()))
		{
			return [] (Block & block, const ColumnNumbers & arguments, const size_t result)
			{
				ConvertImplGenericFromString::execute(block, arguments, result);
			};
		}

		DataTypePtr from_nested_type, to_nested_type;
		auto from_type = typeid_cast<const DataTypeArray *>(from_type_untyped.get());

		/// get the most nested type
		while (from_type && to_type)
		{
			from_nested_type = from_type->getNestedType();
			to_nested_type = to_type->getNestedType();

			from_type = typeid_cast<const DataTypeArray *>(from_nested_type.get());
			to_type = typeid_cast<const DataTypeArray *>(to_nested_type.get());
		}

		/// both from_type and to_type should be nullptr now is array types had same dimensions
		if (from_type || to_type)
			throw Exception{
				"CAST AS Array can only be performed between same-dimensional array types or from String",
				ErrorCodes::TYPE_MISMATCH
			};

		/// Prepare nested type conversion
		const auto nested_function = prepareImpl(from_nested_type, to_nested_type.get());

		return [nested_function, from_nested_type, to_nested_type] (
			Block & block, const ColumnNumbers & arguments, const size_t result)
		{
			auto array_arg = block.safeGetByPosition(arguments.front());

			/// @todo add const variant which retains array constness
			if (const auto col_const_array = typeid_cast<const ColumnConstArray *>(array_arg.column.get()))
				array_arg.column = col_const_array->convertToFullColumn();

			if (auto col_array = typeid_cast<const ColumnArray *>(array_arg.column.get()))
			{
				auto res = new ColumnArray(nullptr, col_array->getOffsetsColumn());
				block.safeGetByPosition(result).column.reset(res);

				/// get the most nested column
				while (const auto nested_col_array = typeid_cast<const ColumnArray *>(col_array->getDataPtr().get()))
				{
					/// create new level of array, copy offsets
					res->getDataPtr() = std::make_shared<ColumnArray>(nullptr, nested_col_array->getOffsetsColumn());

					res = static_cast<ColumnArray *>(res->getDataPtr().get());
					col_array = nested_col_array;
				}

				/// create block for converting nested column containing original and result columns
				Block nested_block{
					{ col_array->getDataPtr(), from_nested_type, "" },
					{ nullptr, to_nested_type, "" }
				};

				const auto nested_result = 1;
				/// convert nested column
				nested_function(nested_block, {0 }, nested_result);

				/// set converted nested column to result
				res->getDataPtr() = nested_block.safeGetByPosition(nested_result).column;
			}
			else
				throw Exception{
					"Illegal column " + array_arg.column->getName() + " for function CAST AS Array",
					ErrorCodes::LOGICAL_ERROR};
		};
	}

	WrapperType createTupleWrapper(const DataTypePtr & from_type_untyped, const DataTypeTuple * to_type)
	{
		/// Conversion from String through parsing.
		if (typeid_cast<const DataTypeString *>(from_type_untyped.get()))
		{
			return [] (Block & block, const ColumnNumbers & arguments, const size_t result)
			{
				ConvertImplGenericFromString::execute(block, arguments, result);
			};
		}

		const auto from_type = typeid_cast<const DataTypeTuple *>(from_type_untyped.get());
		if (!from_type)
			throw Exception{
				"CAST AS Tuple can only be performed between tuple types or from String.\nLeft type: " + from_type_untyped->getName() +
					", right type: " + to_type->getName(),
				ErrorCodes::TYPE_MISMATCH
			};

		if (from_type->getElements().size() != to_type->getElements().size())
			throw Exception{
				"CAST AS Tuple can only be performed between tuple types with the same number of elements or from String.\n"
					"Left type: " + from_type->getName() + ", right type: " + to_type->getName(),
				 ErrorCodes::TYPE_MISMATCH
			};

		const auto & from_element_types = from_type->getElements();
		const auto & to_element_types = to_type->getElements();
		std::vector<WrapperType> element_wrappers;
		element_wrappers.reserve(from_element_types.size());

		/// Create conversion wrapper for each element in tuple
		for (const auto & idx_type : ext::enumerate(from_type->getElements()))
			element_wrappers.push_back(prepareImpl(idx_type.second, to_element_types[idx_type.first].get()));

		auto function_tuple = FunctionTuple::create(context);
		return [element_wrappers, function_tuple, from_element_types, to_element_types]
			(Block & block, const ColumnNumbers & arguments, const size_t result)
		{
			const auto col = block.safeGetByPosition(arguments.front()).column.get();

			/// copy tuple elements to a separate block
			Block element_block;

			/// @todo retain constness
			if (const auto column_tuple = typeid_cast<const ColumnTuple *>(col))
				element_block = column_tuple->getData();
			else if (const auto column_const_tuple = typeid_cast<const ColumnConstTuple *>(col))
				element_block = static_cast<const ColumnTuple &>(*column_const_tuple->convertToTupleOfConstants()).getData();

			/// create columns for converted elements
			for (const auto & to_element_type : to_element_types)
				element_block.insert({ nullptr, to_element_type, "" });

			/// store position for converted tuple
			const auto converted_tuple_pos = element_block.columns();

			/// insert column for converted tuple
			element_block.insert({ nullptr, std::make_shared<DataTypeTuple>(to_element_types), "" });

			const auto converted_element_offset = from_element_types.size();

			/// invoke conversion for each element
			for (const auto & idx_element_wrapper : ext::enumerate(element_wrappers))
				idx_element_wrapper.second(element_block, { idx_element_wrapper.first },
					converted_element_offset + idx_element_wrapper.first);

			/// form tuple from converted elements using FunctionTuple
			function_tuple->execute(element_block,
				ext::collection_cast<ColumnNumbers>(ext::range(converted_element_offset, 2 * converted_element_offset)),
				converted_tuple_pos);

			/// copy FunctionTuple's result from element_block to resulting block
			block.safeGetByPosition(result).column = element_block.safeGetByPosition(converted_tuple_pos).column;
		};
	}

	template <typename FieldType>
	WrapperType createEnumWrapper(const DataTypePtr & from_type, const DataTypeEnum<FieldType> * to_type)
	{
		using EnumType = DataTypeEnum<FieldType>;
		using Function = typename FunctionTo<EnumType>::Type;

		if (const auto from_enum8 = typeid_cast<const DataTypeEnum8 *>(from_type.get()))
			checkEnumToEnumConversion(from_enum8, to_type);
		else if (const auto from_enum16 = typeid_cast<const DataTypeEnum16 *>(from_type.get()))
			checkEnumToEnumConversion(from_enum16, to_type);

		if (typeid_cast<const DataTypeString *>(from_type.get()))
			return createStringToEnumWrapper<ColumnString, EnumType>();
		else if (typeid_cast<const DataTypeFixedString *>(from_type.get()))
			return createStringToEnumWrapper<ColumnFixedString, EnumType>();
		else if (from_type->behavesAsNumber())
		{
			auto function = Function::create(context);

			/// Check conversion using underlying function
			(void) function->getReturnType({ from_type });

			return [function] (Block & block, const ColumnNumbers & arguments, const size_t result) {
				function->execute(block, arguments, result);
			};
		}
		else
			throw Exception{
				"Conversion from " + from_type->getName() + " to " + to_type->getName() +
					" is not supported",
				ErrorCodes::CANNOT_CONVERT_TYPE
			};
	}

	template <typename EnumTypeFrom, typename EnumTypeTo>
	void checkEnumToEnumConversion(const EnumTypeFrom * const from_type, const EnumTypeTo * const to_type)
	{
		const auto & from_values = from_type->getValues();
		const auto & to_values = to_type->getValues();

		using ValueType = std::common_type_t<typename EnumTypeFrom::FieldType, typename EnumTypeTo::FieldType>;
		using NameValuePair = std::pair<std::string, ValueType>;
		using EnumValues = std::vector<NameValuePair>;

		EnumValues name_intersection;
		std::set_intersection(std::begin(from_values), std::end(from_values),
			std::begin(to_values), std::end(to_values), std::back_inserter(name_intersection),
			[] (auto && from, auto && to) { return from.first < to.first; });

		for (const auto & name_value : name_intersection)
		{
			const auto & old_value = name_value.second;
			const auto & new_value = to_type->getValue(name_value.first);
			if (old_value != new_value)
				throw Exception{
					"Enum conversion changes value for element '" + name_value.first +
						"' from " + toString(old_value) + " to " + toString(new_value),
					ErrorCodes::CANNOT_CONVERT_TYPE
				};
		}
	};

	template <typename ColumnStringType, typename EnumType>
	WrapperType createStringToEnumWrapper()
	{
		return [] (Block & block, const ColumnNumbers & arguments, const size_t result)
		{
			const auto first_col = block.safeGetByPosition(arguments.front()).column.get();

			auto & col_with_type_and_name = block.safeGetByPosition(result);
			auto & result_col = col_with_type_and_name.column;
			const auto & result_type = typeid_cast<EnumType &>(*col_with_type_and_name.type);

			if (const auto col = typeid_cast<const ColumnStringType *>(first_col))
			{
				const auto size = col->size();

				auto res = result_type.createColumn();
				auto & out_data = static_cast<typename EnumType::ColumnType &>(*res).getData();
				out_data.resize(size);

				for (const auto i : ext::range(0, size))
					out_data[i] = result_type.getValue(col->getDataAt(i));

				result_col = res;
			}
			else if (const auto const_col = typeid_cast<const ColumnConstString *>(first_col))
			{
				result_col = result_type.createConstColumn(const_col->size(),
					nearestFieldType(result_type.getValue(const_col->getData())));
			}
			else
				throw Exception{
					"Unexpected column " + first_col->getName() + " as first argument of function " +
						name,
					ErrorCodes::LOGICAL_ERROR
				};
		};
	}

	/// Only trivial NULL -> NULL case
	WrapperType createNullWrapper(const DataTypePtr & from_type, const DataTypeNull * to_type)
	{
		if (!typeid_cast<const DataTypeNull *>(from_type.get()))
			throw Exception("Conversion from " + from_type->getName() + " to " + to_type->getName() + " is not supported",
				ErrorCodes::CANNOT_CONVERT_TYPE);

		return [] (Block & block, const ColumnNumbers & arguments, const size_t result)
		{
			// just copy pointer to Null column
			ColumnWithTypeAndName & res_col = block.safeGetByPosition(result);
			const ColumnWithTypeAndName & src_col = block.safeGetByPosition(arguments.front());
			res_col.column = src_col.column;
		};
	}

	/// Actions to be taken when performing a conversion.
	struct Action
	{
		/// If neither the input type nor the output type is nullable or null,
		/// we perform the conversion without any pre and/or processing.
		static constexpr auto NONE = UInt64(0);
		/// The input has a nullable type. We must extract its nested type
		/// before performing any conversion.
		static constexpr auto UNWRAP_NULLABLE_INPUT = UInt64(1) << 0;
		/// The output has a nullable type. We must wrap the result from the
		/// conversion into a ColumnNullable.
		static constexpr auto WRAP_RESULT_INTO_NULLABLE = UInt64(1) << 1;
		/// The input is the NULL value. Before performing any conversion,
		/// we will turn it into a single UInt8 zero value.
		static constexpr auto CONVERT_NULL = UInt64(1) << 2;
	};

	WrapperType prepare(const DataTypePtr & from_type, const IDataType * const to_type, const uint64_t action)
	{
		auto wrapper = prepareImpl((action & Action::CONVERT_NULL) ?
										std::make_shared<DataTypeUInt8>() :
										from_type,
									to_type);

		if (action & Action::WRAP_RESULT_INTO_NULLABLE)
		{
			return [wrapper, action] (Block & block, const ColumnNumbers & arguments, const size_t result)
			{
				/// Create a temporary block on which to perform the operation.
				auto & res = block.safeGetByPosition(result);
				const auto & ret_type = res.type;
				const auto & nullable_type = static_cast<const DataTypeNullable &>(*ret_type);
				const auto & nested_type = nullable_type.getNestedType();

				Block tmp_block;
				if (action & Action::UNWRAP_NULLABLE_INPUT)
					tmp_block = createBlockWithNestedColumns(block, arguments);
				else if (action & Action::CONVERT_NULL)
				{
					/// The input is replaced by a trivial UInt8 column
					/// which contains only one row whose value is 0.
					tmp_block = block;
					auto & elem = tmp_block.getByPosition(arguments[0]);
					elem.column = std::make_shared<ColumnUInt8>(1, 0);
					elem.type = std::make_shared<DataTypeUInt8>();
				}
				else
					tmp_block = block;

				size_t tmp_res_index = block.columns();
				tmp_block.insert({nullptr, nested_type, ""});

				/// Perform the requested conversion.
				wrapper(tmp_block, arguments, tmp_res_index);

				/// Wrap the result into a nullable column.
				ColumnPtr null_map;

				if (action & Action::UNWRAP_NULLABLE_INPUT)
				{
					/// This is a conversion from a nullable to a nullable type.
					/// So we just keep the null map of the input argument.
					const auto & col = block.safeGetByPosition(arguments[0]).column;
					const auto & nullable_col = static_cast<const ColumnNullable &>(*col);
					null_map = nullable_col.getNullMapColumn();
				}
				else if (action & Action::CONVERT_NULL)
				{
					/// A NULL value has been converted to a nullable type.
					null_map = std::make_shared<ColumnUInt8>(block.rows(), 1);
				}
				else
				{
					/// This is a conversion from an ordinary type to a nullable type.
					/// So we create a trivial null map.
					null_map = std::make_shared<ColumnUInt8>(block.rows(), 0);
				}

				const auto & tmp_res = tmp_block.safeGetByPosition(tmp_res_index);
				res.column = std::make_shared<ColumnNullable>(tmp_res.column, null_map);
			};
		}
		else
			return wrapper;
	}

	WrapperType prepareImpl(const DataTypePtr & from_type, const IDataType * const to_type)
	{
		if (const auto to_actual_type = typeid_cast<const DataTypeUInt8 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeUInt16 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeUInt32 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeUInt64 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeInt8 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeInt16 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeInt32 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeInt64 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeFloat32 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeFloat64 *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeDate *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeDateTime *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto to_actual_type = typeid_cast<const DataTypeString *>(to_type))
			return createWrapper(from_type, to_actual_type);
		else if (const auto type_fixed_string = typeid_cast<const DataTypeFixedString *>(to_type))
			return createFixedStringWrapper(from_type, type_fixed_string->getN());
		else if (const auto type_array = typeid_cast<const DataTypeArray *>(to_type))
			return createArrayWrapper(from_type, type_array);
		else if (const auto type_tuple = typeid_cast<const DataTypeTuple *>(to_type))
			return createTupleWrapper(from_type, type_tuple);
		else if (const auto type_enum = typeid_cast<const DataTypeEnum8 *>(to_type))
			return createEnumWrapper(from_type, type_enum);
		else if (const auto type_enum = typeid_cast<const DataTypeEnum16 *>(to_type))
			return createEnumWrapper(from_type, type_enum);
		else if (const auto type_null = typeid_cast<const DataTypeNull *>(to_type))
			return createNullWrapper(from_type, type_null);

		/// It's possible to use ConvertImplGenericFromString to convert from String to AggregateFunction,
		///  but it is disabled because deserializing aggregate functions state might be unsafe.

		throw Exception{
			"Conversion from " + from_type->getName() + " to " + to_type->getName() +
				" is not supported",
			ErrorCodes::CANNOT_CONVERT_TYPE
		};
	}

	template <typename DataType> static auto monotonicityForType(const DataType * const)
	{
		return FunctionTo<DataType>::Type::Monotonic::get;
	}

	void prepareMonotonicityInformation(const DataTypePtr & from_type, const IDataType * to_type)
	{
		if (const auto type = typeid_cast<const DataTypeUInt8 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeUInt16 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeUInt32 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeUInt64 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeInt8 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeInt16 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeInt32 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeInt64 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeFloat32 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeFloat64 *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeDate *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeDateTime *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (const auto type = typeid_cast<const DataTypeString *>(to_type))
			monotonicity_for_range = monotonicityForType(type);
		else if (from_type->isNumeric())
		{
			if (const auto type = typeid_cast<const DataTypeEnum8 *>(to_type))
				monotonicity_for_range = monotonicityForType(type);
			else if (const auto type = typeid_cast<const DataTypeEnum16 *>(to_type))
				monotonicity_for_range = monotonicityForType(type);
		}
		/// other types like FixedString, Array and Tuple have no monotonicity defined
	}

public:
	static constexpr auto name = "CAST";
	static FunctionPtr create(const Context & context) { return std::make_shared<FunctionCast>(context); }

	String getName() const override { return name; }

	bool hasSpecialSupportForNulls() const override { return true; }

	size_t getNumberOfArguments() const override { return 2; }

	void getReturnTypeAndPrerequisitesImpl(
		const ColumnsWithTypeAndName & arguments, DataTypePtr & out_return_type,
		std::vector<ExpressionAction> & out_prerequisites) override
	{
		const auto type_col = typeid_cast<const ColumnConstString *>(arguments.back().column.get());
		if (!type_col)
			throw Exception("Second argument to " + getName() + " must be a constant string describing type",
				ErrorCodes::ILLEGAL_TYPE_OF_ARGUMENT);

		out_return_type = DataTypeFactory::instance().get(type_col->getData());

		/// Determine whether pre-processing and/or post-processing must take
		/// place during conversion.
		uint64_t action = Action::NONE;
		const auto & from_type = arguments.front().type;

		if (from_type->isNullable())
			action |= Action::UNWRAP_NULLABLE_INPUT;
		else if (from_type->isNull() && !out_return_type->isNull())
			action |= Action::CONVERT_NULL;

		if (out_return_type->isNullable())
			action |= Action::WRAP_RESULT_INTO_NULLABLE;

		/// Check that the requested conversion is allowed.
		if (!(action & Action::WRAP_RESULT_INTO_NULLABLE))
		{
			if (action & Action::CONVERT_NULL)
				throw Exception{"Cannot convert NULL into a non-nullable type",
					ErrorCodes::CANNOT_CONVERT_TYPE};
			else if (action & Action::UNWRAP_NULLABLE_INPUT)
				throw Exception{"Cannot convert data from a nullable type to a non-nullable type",
					ErrorCodes::CANNOT_CONVERT_TYPE};
		}

		DataTypePtr from_inner_type;
		const IDataType * to_inner_type;

		/// Create the requested conversion.
		if (action & Action::WRAP_RESULT_INTO_NULLABLE)
		{
			if (action & Action::UNWRAP_NULLABLE_INPUT)
			{
				const auto & nullable_type = static_cast<const DataTypeNullable &>(*from_type);
				from_inner_type = nullable_type.getNestedType();
			}
			else
				from_inner_type = from_type;

			const auto & nullable_type = static_cast<const DataTypeNullable &>(*out_return_type);
			to_inner_type = nullable_type.getNestedType().get();
		}
		else
		{
			from_inner_type = from_type;
			to_inner_type = out_return_type.get();
		}

		wrapper_function = prepare(from_inner_type, to_inner_type, action);
		prepareMonotonicityInformation(from_inner_type, to_inner_type);
	}

	void executeImpl(Block & block, const ColumnNumbers & arguments, const size_t result) override
	{
		/// drop second argument, pass others
		ColumnNumbers new_arguments{arguments.front()};
		if (arguments.size() > 2)
			new_arguments.insert(std::end(new_arguments), std::next(std::begin(arguments), 2), std::end(arguments));

		wrapper_function(block, new_arguments, result);
	}

	bool hasInformationAboutMonotonicity() const override
	{
		return static_cast<bool>(monotonicity_for_range);
	}

	Monotonicity getMonotonicityForRange(const IDataType & type, const Field & left, const Field & right) const override
	{
		return monotonicity_for_range(type, left, right);
	}
};

}