SQL Server Native Client Date and Time Improvements
This topic describes the SQL Server Native Client support for the date and time data types that were added in SQL Server 2008.
For information about sample applications that demonstrate this feature, see SQL Server Data Programming Samples.
The following sections describe various ways of using the new date and time types.
Use Date as a Distinct Data Type
Beginning with SQL Server 2008, enhanced support for date/time types makes it more efficient to use the SQL_TYPE_DATE ODBC type (SQL_DATE for ODBC 2.0 applications) and the DBTYPE_DBDATE OLE DB type.
Use Time as a Distinct Data Type
OLE DB already has a data type that just contains the time, DBTYPE_DBTIME, which has a precision of 1 second. In ODBC, the equivalent type is SQL_TYPE_TIME (SQL_TIME for ODBC 2.0 applications).
The new SQL Server time data type has fractional seconds accurate to 100 nanoseconds. This requires new types in SQL Server Native Client: DBTYPE_DBTIME2 (OLE DB) and SQL_SS_TIME2 (ODBC). Existing applications written to use times with no fractional seconds can use time(0) columns. The existing OLE DB DBTYPE_TIME and ODBC SQL_TYPE_TIME types and their corresponding structs should work correctly, unless the applications rely on the type returned in metadata.
Use Time as a Distinct Data Type with Extended Fractional Seconds Precision
Some applications, such as process control and manufacturing applications, require the ability to handle time data with a precision of up to 100 nanoseconds. New types for this purpose are DBTYPE_DBTIME2 (OLE DB) and SQL_SS_TIME2 (ODBC).
Use Datetime with Extended Fractional Seconds Precision
OLE DB already defines a type with a precision of up to 1 nanosecond. However, this type is already used by existing SQL Server applications and such applications have an expectation of only 1/300 of a second precision. The new datetime2(3) type is not directly compatible with the existing datetime type. If there is a risk that this will affect application behavior, applications must use a new DBCOLUMN flag to determine the actual server type.
ODBC also defines a type with a precision of up to 1 nanosecond. However, this type is already used by existing SQL Server applications and such applications expect only 3 millisecond precision. The new datetime2(3) type is not directly compatible with the existing datetime type. datetime2(3) has a precision of one millisecond, and datetime has a precision of 1/300 of a second. In ODBC, applications can determine which server type is in use with the descriptor field SQL_DESC_TYPE_NAME. Therefore, the existing type SQL_TYPE_TIMESTAMP (SQL_TIMESTAMP for ODBC 2.0 applications) can be used for both types.
Use Datetime with Extended Fractional Seconds Precision and Timezone
Some applications require datetime values with timezone information. This is supported by the new DBTYPE_DBTIMESTAMPOFFSET (OLE DB) and SQL_SS_TIMESTAMPOFFSET (ODBC) types.
Use Date/Time/Datetime/Datetimeoffset Data with Client-Side Conversions Consistent with Existing Conversions
The ODBC standard describes how conversions between existing date, time, and timestamp types work. These are extended in a consistent manner to include conversions between all date and time types introduced in SQL Server 2008.