ClickHouse/dbms/src/Functions/IFunction.cpp

#include <DB/Functions/IFunction.h>
#include <DB/Columns/ColumnConst.h>
#include <DB/Columns/ColumnNullable.h>
#include <DB/DataTypes/DataTypeNull.h>
#include <DB/DataTypes/DataTypeNullable.h>
#include <DB/Interpreters/ExpressionActions.h>

namespace DB
{

namespace
{

/// Suppose a function which has no special support for nullable arguments
/// has been called with arguments, one or more of them being nullable.
/// Then the method below endows the result, which is nullable, with a null
/// byte map that is determined by OR-ing the null byte maps of the nullable
/// arguments.
void createNullValuesByteMap(Block & block, const ColumnNumbers & args, size_t result)
{
	ColumnNullable & res_col = static_cast<ColumnNullable &>(*block.unsafeGetByPosition(result).column);

	for (const auto & arg : args)
	{
		const ColumnWithTypeAndName & elem = block.unsafeGetByPosition(arg);
		if (elem.column->isNullable())
		{
			const ColumnNullable & nullable_col = static_cast<const ColumnNullable &>(*elem.column);
			res_col.applyNullValuesByteMap(nullable_col);
		}
	}
}

/// In a set of objects (columns of a block / set of columns / set of data types),
/// are there any "special" (i.e. nullable or null) objects?
enum class Category
{
	/// No nullable objects. No null objects.
	IS_ORDINARY = 0,
	/// At least one nullable object. No null objects.
	IS_NULLABLE,
	/// At least one null object.
	IS_NULL
};

/// Check if a block contains at least one special column, in the sense
/// defined above, among the specified columns.
Category blockHasSpecialColumns(const Block & block, const ColumnNumbers & args)
{
	bool found_nullable = false;
	bool found_null = false;

	for (const auto & arg : args)
	{
		const auto & elem = block.unsafeGetByPosition(arg);

		if (!found_null && elem.column->isNull())
		{
			found_null = true;
			break;
		}
		else if (!found_nullable && elem.column->isNullable())
			found_nullable = true;
	}

	if (found_null)
		return Category::IS_NULL;
	else if (found_nullable)
		return Category::IS_NULLABLE;
	else
		return Category::IS_ORDINARY;
}

/// Check if at least one column is special in the sense defined above.
Category hasSpecialColumns(const ColumnsWithTypeAndName & args)
{
	bool found_nullable = false;
	bool found_null = false;

	for (const auto & arg : args)
	{
		if (!found_null && arg.type->isNull())
		{
			found_null = true;
			break;
		}
		else if (!found_nullable && arg.type->isNullable())
			found_nullable = true;
	}

	if (found_null)
		return Category::IS_NULL;
	else if (found_nullable)
		return Category::IS_NULLABLE;
	else
		return Category::IS_ORDINARY;
}

/// Check if at least one data type is special in the sense defined above.
Category hasSpecialDataTypes(const DataTypes & args)
{
	bool found_nullable = false;
	bool found_null = false;

	for (const auto & arg : args)
	{
		if (!found_null && arg->isNull())
		{
			found_null = true;
			break;
		}
		else if (!found_nullable && arg->isNullable())
			found_nullable = true;
	}

	if (found_null)
		return Category::IS_NULL;
	else if (found_nullable)
		return Category::IS_NULLABLE;
	else
		return Category::IS_ORDINARY;
}

/// Turn the specified set of columns into their respective nested columns.
ColumnsWithTypeAndName toNestedColumns(const ColumnsWithTypeAndName & args)
{
	ColumnsWithTypeAndName new_args;
	new_args.reserve(args.size());

	for (const auto & arg : args)
	{
		if (arg.type->isNullable())
		{
			auto nullable_col = static_cast<const ColumnNullable *>(arg.column.get());
			ColumnPtr nested_col = (nullable_col != nullptr) ? nullable_col->getNestedColumn() : nullptr;
			auto nullable_type = static_cast<const DataTypeNullable *>(arg.type.get());
			DataTypePtr nested_type = nullable_type->getNestedType();

			new_args.emplace_back(nested_col, nested_type, arg.name);
		}
		else
			new_args.emplace_back(arg.column, arg.type, arg.name);
	}

	return new_args;
}

/// Turn the specified set of data types into their respective nested data types.
DataTypes toNestedDataTypes(const DataTypes & args)
{
	DataTypes new_args;
	new_args.reserve(args.size());

	for (const auto & arg : args)
	{
		if (arg->isNullable())
		{
			auto nullable_type = static_cast<const DataTypeNullable *>(arg.get());
			DataTypePtr nested_type = nullable_type->getNestedType();
			new_args.push_back(nested_type);
		}
		else
			new_args.push_back(arg);
	}

	return new_args;
}

}

DataTypePtr IFunction::getReturnType(const DataTypes & arguments) const
{
	auto category = hasSpecialDataTypes(arguments);

	if (category == Category::IS_ORDINARY)
	{
	}
	else if (category == Category::IS_NULL)
	{
		if (!hasSpecialSupportForNulls())
			return std::make_shared<DataTypeNull>();
	}
	else if (category == Category::IS_NULLABLE)
	{
		if (!hasSpecialSupportForNulls())
		{
			const DataTypes new_args = toNestedDataTypes(arguments);
			return getReturnTypeImpl(new_args);
		}
	}
	else
		throw Exception{"IFunction: internal error", ErrorCodes::LOGICAL_ERROR};

	return getReturnTypeImpl(arguments);
}

void IFunction::getReturnTypeAndPrerequisites(
	const ColumnsWithTypeAndName & arguments,
	DataTypePtr & out_return_type,
	std::vector<ExpressionAction> & out_prerequisites)
{
	auto category = hasSpecialColumns(arguments);

	if (category == Category::IS_ORDINARY)
	{
	}
	else if (category == Category::IS_NULL)
	{
		if (!hasSpecialSupportForNulls())
		{
			out_return_type = std::make_shared<DataTypeNull>();
			return;
		}
	}
	else if (category == Category::IS_NULLABLE)
	{
		if (!hasSpecialSupportForNulls())
		{
			const ColumnsWithTypeAndName new_args = toNestedColumns(arguments);
			getReturnTypeAndPrerequisitesImpl(new_args, out_return_type, out_prerequisites);
			out_return_type = std::make_shared<DataTypeNullable>(out_return_type);
			return;
		}
	}
	else
		throw Exception{"IFunction: internal error", ErrorCodes::LOGICAL_ERROR};

	getReturnTypeAndPrerequisitesImpl(arguments, out_return_type, out_prerequisites);
}

void IFunction::getLambdaArgumentTypes(DataTypes & arguments) const
{
	auto category = hasSpecialDataTypes(arguments);

	if (category == Category::IS_ORDINARY)
	{
	}
	else if (category == Category::IS_NULL)
	{
		if (!hasSpecialSupportForNulls())
			return;
	}
	else if (category == Category::IS_NULLABLE)
	{
		if (!hasSpecialSupportForNulls())
		{
			DataTypes new_args = toNestedDataTypes(arguments);
			getLambdaArgumentTypesImpl(new_args);
			arguments = std::move(new_args);
			return;
		}
	}
	else
		throw Exception{"IFunction: internal error", ErrorCodes::LOGICAL_ERROR};

	getLambdaArgumentTypesImpl(arguments);
}

void IFunction::execute(Block & block, const ColumnNumbers & args, size_t result)
{
	auto strategy = chooseStrategy(block, args);
	Block processed_block = preProcessBlock(strategy, block, args);

	if (strategy != RETURN_NULL)
	{
		Block & src = processed_block ? processed_block : block;
		executeImpl(src, args, result);
	}

	postProcessResult(strategy, block, processed_block, args, result);
}

void IFunction::execute(Block & block, const ColumnNumbers & args, const ColumnNumbers & prerequisites, size_t result)
{
	auto strategy = chooseStrategy(block, args);
	Block processed_block = preProcessBlock(strategy, block, args);

	if (strategy != RETURN_NULL)
	{
		Block & src = processed_block ? processed_block : block;
		executeImpl(src, args, prerequisites, result);
	}

	postProcessResult(strategy, block, processed_block, args, result);
}

IFunction::Strategy IFunction::chooseStrategy(const Block & block, const ColumnNumbers & args)
{
	auto category = blockHasSpecialColumns(block, args);

	if (category == Category::IS_ORDINARY)
	{
	}
	else if (category == Category::IS_NULL)
	{
		if (!hasSpecialSupportForNulls())
			return RETURN_NULL;
	}
	else if (category == Category::IS_NULLABLE)
	{
		if (!hasSpecialSupportForNulls())
			return PROCESS_NULLABLE_COLUMNS;
	}
	else
		throw Exception{"IFunction: internal error", ErrorCodes::LOGICAL_ERROR};

	return DIRECTLY_EXECUTE;
}

Block IFunction::preProcessBlock(Strategy strategy, const Block & block, const ColumnNumbers & args)
{
	if (strategy == DIRECTLY_EXECUTE)
		return {};
	else if (strategy == RETURN_NULL)
		return {};
	else if (strategy == PROCESS_NULLABLE_COLUMNS)
	{
		/// Run the function on a block whose nullable columns have been replaced
		/// with their respective nested columns.
		return createBlockWithNestedColumns(block, args);
	}
	else
		throw Exception{"IFunction: internal error", ErrorCodes::LOGICAL_ERROR};
}

void IFunction::postProcessResult(Strategy strategy, Block & block, const Block & processed_block,
	const ColumnNumbers & args, size_t result)
{
	if (strategy == DIRECTLY_EXECUTE)
	{
	}
	else if (strategy == RETURN_NULL)
	{
		/// We have found at least one NULL argument. Therefore we return NULL.
		ColumnWithTypeAndName & dest_col = block.getByPosition(result);
		dest_col.column =  std::make_shared<ColumnNull>(block.rowsInFirstColumn(), Null());
	}
	else if (strategy == PROCESS_NULLABLE_COLUMNS)
	{
		/// Initialize the result column.
		const ColumnWithTypeAndName & source_col = processed_block.getByPosition(result);
		ColumnWithTypeAndName & dest_col = block.getByPosition(result);
		dest_col.column = std::make_shared<ColumnNullable>(source_col.column);

		/// Make a null map for the result.
		ColumnNullable & nullable_col = static_cast<ColumnNullable &>(*dest_col.column);
		nullable_col.getNullValuesByteMap() = std::make_shared<ColumnUInt8>(dest_col.column->size(), 0);
		createNullValuesByteMap(block, args, result);
	}
	else
		throw Exception{"IFunction: internal error", ErrorCodes::LOGICAL_ERROR};
}

/// Return a copy of a given block in which the specified columns are replaced by
/// their respective nested columns if they are nullable.
Block IFunction::createBlockWithNestedColumns(const Block & block, ColumnNumbers args)
{
	std::sort(args.begin(), args.end());

	Block res;

	size_t j = 0;
	for (size_t i = 0; i < block.columns(); ++i)
	{
		const auto & col = block.unsafeGetByPosition(i);
		bool is_inserted = false;

		if (i == args[j])
		{
			++j;

			if (col.column->isNullable())
			{
				auto nullable_col = static_cast<const ColumnNullable *>(col.column.get());
				ColumnPtr nested_col = nullable_col->getNestedColumn();

				auto nullable_type = static_cast<const DataTypeNullable *>(col.type.get());
				DataTypePtr nested_type = nullable_type->getNestedType();

				res.insert(i, {nested_col, nested_type, col.name});

				is_inserted = true;
			}
		}

		if (!is_inserted)
			res.insert(i, col);
	}

	return res;
}

}