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#include <Columns/ColumnLowCardinality.h>
#include <Columns/ColumnNullable.h>
#include <Core/ColumnNumbers.h>
#include <DataTypes/DataTypeNothing.h>
#include <DataTypes/DataTypeNullable.h>
#include <DataTypes/DataTypesNumber.h>
#include <DataTypes/getLeastSupertype.h>
#include <Functions/FunctionFactory.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/IFunction.h>
namespace DB
{
namespace
{
/// Implements the function coalesce which takes a set of arguments and
/// returns the value of the leftmost non-null argument. If no such value is
/// found, coalesce() returns NULL.
class FunctionCoalesce : public IFunction
{
public:
static constexpr auto name = "coalesce";
static FunctionPtr create(ContextPtr context)
{
return std::make_shared<FunctionCoalesce>(context);
}
explicit FunctionCoalesce(ContextPtr context_) : context(context_) {}
std::string getName() const override
{
return name;
}
bool useDefaultImplementationForNulls() const override { return false; }
bool isVariadic() const override { return true; }
bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
size_t getNumberOfArguments() const override { return 0; }
ColumnNumbers getArgumentsThatDontImplyNullableReturnType(size_t number_of_arguments) const override
{
ColumnNumbers args;
for (size_t i = 0; i + 1 < number_of_arguments; ++i)
args.push_back(i);
return args;
}
DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
{
/// Skip all NULL arguments. If any argument is non-Nullable, skip all next arguments.
DataTypes filtered_args;
filtered_args.reserve(arguments.size());
for (const auto & arg : arguments)
{
if (arg->onlyNull())
continue;
filtered_args.push_back(arg);
if (!arg->isNullable())
break;
}
DataTypes new_args;
for (size_t i = 0; i < filtered_args.size(); ++i)
{
bool is_last = i + 1 == filtered_args.size();
if (is_last)
new_args.push_back(filtered_args[i]);
else
new_args.push_back(removeNullable(filtered_args[i]));
}
if (new_args.empty())
return std::make_shared<DataTypeNullable>(std::make_shared<DataTypeNothing>());
if (new_args.size() == 1)
return new_args.front();
auto res = getLeastSupertype(new_args);
/// if last argument is not nullable, result should be also not nullable
if (!new_args.back()->isNullable() && res->isNullable())
res = removeNullable(res);
return res;
}
ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, size_t input_rows_count) const override
{
/// coalesce(arg0, arg1, ..., argN) is essentially
/// multiIf(isNotNull(arg0), assumeNotNull(arg0), isNotNull(arg1), assumeNotNull(arg1), ..., argN)
/// with constant NULL arguments removed.
ColumnsWithTypeAndName filtered_args;
filtered_args.reserve(arguments.size());
for (const auto & arg : arguments)
{
const auto & type = arg.type;
if (type->onlyNull())
continue;
filtered_args.push_back(arg);
if (!type->isNullable())
break;
}
auto is_not_null = FunctionFactory::instance().get("isNotNull", context);
auto assume_not_null = FunctionFactory::instance().get("assumeNotNull", context);
ColumnsWithTypeAndName multi_if_args;
ColumnsWithTypeAndName tmp_args(1);
for (size_t i = 0; i < filtered_args.size(); ++i)
{
bool is_last = i + 1 == filtered_args.size();
if (is_last)
{
multi_if_args.push_back(filtered_args[i]);
}
else
{
tmp_args[0] = filtered_args[i];
auto & cond = multi_if_args.emplace_back(ColumnWithTypeAndName{nullptr, std::make_shared<DataTypeUInt8>(), ""});
cond.column = is_not_null->build(tmp_args)->execute(tmp_args, cond.type, input_rows_count);
tmp_args[0] = filtered_args[i];
auto & val = multi_if_args.emplace_back(ColumnWithTypeAndName{nullptr, removeNullable(filtered_args[i].type), ""});
val.column = assume_not_null->build(tmp_args)->execute(tmp_args, val.type, input_rows_count);
}
}
/// If all arguments appeared to be NULL.
if (multi_if_args.empty())
return result_type->createColumnConstWithDefaultValue(input_rows_count);
if (multi_if_args.size() == 1)
return multi_if_args.front().column;
/// If there was only two arguments (3 arguments passed to multiIf)
/// use function "if" instead, because it's implemented more efficient.
/// TODO: make "multiIf" the same efficient.
FunctionOverloadResolverPtr if_function;
if (multi_if_args.size() == 3)
if_function = FunctionFactory::instance().get("if", context);
else
if_function = FunctionFactory::instance().get("multiIf", context);
ColumnPtr res = if_function->build(multi_if_args)->execute(multi_if_args, result_type, input_rows_count);
/// if last argument is not nullable, result should be also not nullable
if (!multi_if_args.back().column->isNullable() && res->isNullable())
{
if (const auto * column_lc = checkAndGetColumn<ColumnLowCardinality>(*res))
res = checkAndGetColumn<ColumnNullable>(*column_lc->convertToFullColumn())->getNestedColumnPtr();
else if (const auto * column_const = checkAndGetColumn<ColumnConst>(*res))
res = checkAndGetColumn<ColumnNullable>(column_const->getDataColumn())->getNestedColumnPtr();
else
res = checkAndGetColumn<ColumnNullable>(*res)->getNestedColumnPtr();
}
return res;
}
private:
ContextPtr context;
};
}
REGISTER_FUNCTION(Coalesce)
{
factory.registerFunction<FunctionCoalesce>({}, FunctionFactory::CaseInsensitive);
}
}
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