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Applies to: 
SQL Server
If you're familiar with the SQL Server data types, you find similar semantics and precision in the System.Data.SqlTypes namespace in the .NET Framework. There are some differences, however, and this article covers the most important of these differences.
Null values
A primary difference between native common language runtime (CLR) data types and SQL Server data types is that the former don't allow for NULL values, while the latter provide full NULL semantics.
Comparisons are affected by NULL values. When you compare two values x and y, if either x or y is NULL, then some logical comparisons evaluate to an UNKNOWN value rather than true or false.
SqlBoolean data type
The System.Data.SqlTypes namespace introduces a SqlBoolean type to represent this three-value logic. Comparisons between any SqlTypes return a SqlBoolean value type. The UNKNOWN value is represented by the null value of the SqlBoolean type. The properties IsTrue, IsFalse, and IsNull are provided to check the value of a SqlBoolean type.
Operations, functions, and null values
All arithmetic operators (+, -, *, /, %), bitwise operators (~, &, and |), and most functions return NULL if any of the operands or arguments of SqlTypes are null. The IsNull property always returns a true or false value.
Precision
Decimal data types in the .NET Framework CLR have different maximum values than numeric and decimal data types in SQL Server. In addition, in the .NET Framework CLR decimal data types assume the maximum precision. In the CLR for SQL Server, however, SqlDecimal provides the same maximum precision and scale, and the same semantics as the decimal data type in SQL Server.
Overflow detection
In the .NET Framework CLR, the addition of two very large numbers might not throw an exception. Instead, if no check operator is used, the returned result might wrap around as a negative integer. In System.Data.SqlTypes, exceptions are thrown for all overflow and underflow errors, and divide-by-zero errors.