ClickHouse/dbms/src/Functions/nullIf.cpp

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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
{
/// 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:
const Context & context;
public:
static constexpr auto name = "nullIf";
static FunctionPtr create(const Context & context)
{
return std::make_shared<FunctionNullIf>(context);
}
FunctionNullIf(const Context & 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; }
DataTypePtr getReturnTypeImpl(const DataTypes & arguments) const override
{
return makeNullable(arguments[0]);
}
void executeImpl(Block & block, const ColumnNumbers & arguments, size_t result, size_t input_rows_count) override
{
/// nullIf(col1, col2) == if(col1 == col2, NULL, col1)
Block temp_block = block;
size_t res_pos = temp_block.columns();
temp_block.insert({nullptr, std::make_shared<DataTypeUInt8>(), ""});
{
auto equals_func = FunctionFactory::instance().get("equals", context)->build(
{temp_block.getByPosition(arguments[0]), temp_block.getByPosition(arguments[1])});
equals_func->execute(temp_block, {arguments[0], arguments[1]}, res_pos, input_rows_count);
}
/// Argument corresponding to the NULL value.
size_t null_pos = temp_block.columns();
/// Append a NULL column.
ColumnWithTypeAndName null_elem;
null_elem.type = block.getByPosition(result).type;
null_elem.column = null_elem.type->createColumnConstWithDefaultValue(input_rows_count);
null_elem.name = "NULL";
temp_block.insert(null_elem);
auto func_if = FunctionFactory::instance().get("if", context)->build(
{temp_block.getByPosition(res_pos), temp_block.getByPosition(null_pos), temp_block.getByPosition(arguments[0])});
func_if->execute(temp_block, {res_pos, null_pos, arguments[0]}, result, input_rows_count);
block.getByPosition(result).column = std::move(temp_block.getByPosition(result).column);
}
};
void registerFunctionNullIf(FunctionFactory & factory)
{
factory.registerFunction<FunctionNullIf>(FunctionFactory::CaseInsensitive);
}
}