4.9. SQL Server Data Types in the .NET Framework

The System.Data.SqlTypes namespace is part of the base class library of the .NET Framework. The namespace provides data types that map closely to native SQL Server data types. There are differences between SqlTypes data types and .NET Framework data types:

• SqlTypes data types support NULL values while .NET Framework data types do not. All arithmetic and bitwise operators and most functions return NULL if any SqlTypes operands or arguments are NULL.

• SqlTypes provides a SqlBoolean data type that represents a tristate logical value—true, false, and null (unknown value).

• The .NET Framework Decimal data type and the corresponding SQL Server Decimal data type have different maximum values. The Decimal data type assumes maximum precision, whereas the SqlDecimal data type and the SQL Server Decimal data type have the same maximum precision, scale, and semantics.

• Exceptions are thrown for all overflow and underflow errors and divide-by-zero errors when using SqlTypes data types. This behavior is not guaranteed with .NET Framework data types.

Table 4-16 lists SQL Server data types and their equivalents in the System.Data.SqlTypes namespace and in the .NET Framework.

Table 4-16. SQL Server, System.Data.SqlTypes, and .NET Framework data type equivalents

SQL Server data type	System.Data.SqlTypes data type	.NET Framework data type
varbinary	SqlBytes, SqlBinary	Byte[]
binary	SqlBytes, SqlBinary	Byte[]
image	None	None
varchar	None	None
char	None	None
nvarchar	SqlChars, SqlString	String, Char[]
nchar	SqlChars, SqlString	String, Char[]
text	None	None
ntext	None	None
uniqueidentifier	SqlGuid	Guid
rowversion	None	Byte[]
bit	SqlBoolean	Boolean
tinyint	SqlByte	Byte
smallint	SqlInt16	Int16
int	SqlInt32	Int32
bigint	SqlInt64	Int64
smallmoney	SqlMoney	Decimal
money	SqlMoney	Decimal
numeric	SqlDecimal	Decimal
decimal	SqlDecimal	Decimal
real	SqlSingle	Single
float	SqlDouble	Double
smalldatetime	SqlDateTime	DateTime
datetime	SqlDateTime	DateTime
sql_variant	None	Object
User-defined type (UDT)	None	Same class bound to the type in the registered assembly or dependent assembly
table	None	None
cursor	None	None
timestamp	None	None
xml	SqlXml	None