Nullable Data Types

In .NET types that cannot be null such as int are called value types. Types that can have a null value such as string are called reference types. Sometimes it is convenient though to value that is an value type but that that can also have a null value. These types are called nullable types.

Using nullable types in C# code

// This is C# code, not U-SQL
int? i = 100;
i = 200;
i = null;

Supported nullable types

U-SQL supports the following nullable types

byte?
sbyte?
int?
uint?
long?
ulong?
float?
double?
decimal?
short?
ushort?
bool?
Guid?
DateTime?
char?

Nullable types don't apply to reference types such as string

The purpose of "nullable" is enable null values for a type that doesn't already support null values. The string type - like all .NET reference types - already supports null values.