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Part 2: The 32-Bit/64-Bit Drivers : The SQL Server Legacy Wire Protocol Driver : Unicode Support
  
Unicode Support
The SQL Server Legacy Wire Protocol driver maps the Microsoft SQL Server data types to Unicode data types as shown in the following table:
SQL Server Data Type
Mapped to. . .
nchar
SQL_WCHAR
ntext
SQL_WLONGVARCHAR
nvarchar
SQL_WVARCHAR
nvarchar(max) 1
SQL_WLONGVARCHAR
sysname
SQL_WVARCHAR
xml 2
SQL_WLONGVARCHAR
1 Supported only for Microsoft SQL Server 2005 and higher.

2 Supported only for Microsoft SQL Server 2005 and higher.

The driver supports the Unicode ODBC W (Wide) function calls, such as SQLConnectW. This allows the Driver Manager to transmit these calls directly to the driver. Otherwise, the Driver Manager would incur the additional overhead of converting the W calls to ANSI function calls, and vice versa.
See UTF-16 Applications on UNIX and Linux for related details. Also, refer to "Internationalization, Localization, and Unicode" in the DataDirect Connect Series for ODBC Reference for a more detailed explanation of Unicode.