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#include <Functions/IFunction.h>
#include <Functions/FunctionHelpers.h>
#include <Functions/FunctionFactory.h>
#include <DataTypes/DataTypesNumber.h>
#include <DataTypes/DataTypeNullable.h>
#include <DataTypes/getLeastSupertype.h>
#include <Core/ColumnNumbers.h>
#include <Columns/ColumnNullable.h>
namespace DB
{
namespace
{
/// Implements the function ifNull which takes 2 arguments and returns
/// the value of the 1st argument if it is not null. Otherwise it returns
/// the value of the 2nd argument.
class FunctionIfNull : public IFunction
{
public:
static constexpr auto name = "ifNull";
explicit FunctionIfNull(ContextPtr context_) : context(context_) {}
static FunctionPtr create(ContextPtr context)
{
return std::make_shared<FunctionIfNull>(context);
}
std::string getName() const override
{
return name;
}
size_t getNumberOfArguments() const override { return 2; }
bool useDefaultImplementationForNulls() const override { return false; }
bool useDefaultImplementationForConstants() const override { return true; }
bool isSuitableForShortCircuitArgumentsExecution(const DataTypesWithConstInfo & /*arguments*/) const override { return false; }
ColumnNumbers getArgumentsThatDontImplyNullableReturnType(size_t /*number_of_arguments*/) const override { return {0}; }
DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
{
if (arguments[0]->onlyNull())
return arguments[1];
if (!arguments[0]->isNullable())
return arguments[0];
return getLeastSupertype(DataTypes{removeNullable(arguments[0]), arguments[1]});
}
ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, size_t input_rows_count) const override
{
/// Always null.
if (arguments[0].type->onlyNull())
return arguments[1].column;
/// Could not contain nulls, so nullIf makes no sense.
if (!arguments[0].type->isNullable())
return arguments[0].column;
/// ifNull(col1, col2) == if(isNotNull(col1), assumeNotNull(col1), col2)
ColumnsWithTypeAndName columns{arguments[0]};
auto is_not_null = FunctionFactory::instance().get("isNotNull", context)->build(columns);
auto is_not_null_type = std::make_shared<DataTypeUInt8>();
auto is_not_null_res = is_not_null->execute(columns, is_not_null_type, input_rows_count);
auto assume_not_null = FunctionFactory::instance().get("assumeNotNull", context)->build(columns);
auto assume_not_null_type = removeNullable(arguments[0].type);
auto assume_nut_null_res = assume_not_null->execute(columns, assume_not_null_type, input_rows_count);
ColumnsWithTypeAndName if_columns
{
{is_not_null_res, is_not_null_type, ""},
{assume_nut_null_res, assume_not_null_type, ""},
arguments[1],
};
auto func_if = FunctionFactory::instance().get("if", context)->build(if_columns);
return func_if->execute(if_columns, result_type, input_rows_count);
}
private:
ContextPtr context;
};
}
REGISTER_FUNCTION(IfNull)
{
factory.registerFunction<FunctionIfNull>({}, FunctionFactory::CaseInsensitive);
}
}
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