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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 <Core/ColumnNumbers.h>
#include <Columns/ColumnNullable.h>
namespace DB
{
namespace
{
/// Implements the function nullIf which takes 2 arguments and returns
/// NULL if both arguments have the same value. Otherwise it returns the
/// value of the first argument.
class FunctionNullIf : public IFunction
{
private:
ContextPtr context;
public:
static constexpr auto name = "nullIf";
static FunctionPtr create(ContextPtr context)
{
return std::make_shared<FunctionNullIf>(context);
}
explicit FunctionNullIf(ContextPtr context_) : context(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; }
DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
{
return makeNullable(arguments[0]);
}
ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, size_t input_rows_count) const override
{
/// nullIf(col1, col2) == if(col1 = col2, NULL, col1)
auto equals_func = FunctionFactory::instance().get("equals", context)->build(arguments);
auto eq_res = equals_func->execute(arguments, equals_func->getResultType(), input_rows_count);
ColumnsWithTypeAndName if_columns
{
{eq_res, equals_func->getResultType(), ""},
{result_type->createColumnConstWithDefaultValue(input_rows_count), result_type, "NULL"},
arguments[0],
};
auto func_if = FunctionFactory::instance().get("if", context)->build(if_columns);
auto if_res = func_if->execute(if_columns, result_type, input_rows_count);
return makeNullable(if_res);
}
};
}
REGISTER_FUNCTION(NullIf)
{
factory.registerFunction<FunctionNullIf>({}, FunctionFactory::CaseInsensitive);
}
}
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