Connecting Early Version Clients to SQL Server 7.0

Microsoft® SQL Server™ version 7.0 supports connections from client applications that use earlier 7.0 versions of the SQL Server client software. SQL Server 7.0 supports these connections in a compatibility mode. If a database is migrated to version 7.0 from versions 4.21a, 6.0, or 6.5, the applications using the database can continue working with few, if any, changes.

Applications using version 4.21a, 6.0, or 6.5 of the SQL Server client software use version 4.2 of the SQL Server Tabular Data Stream (TDS) protocol to communicate with SQL Server. Applications using SQL Server 7.0 versions of the client software use TDS version 7.0.

Applications using TDS 4.2 cannot access all features introduced in SQL Server 7.0. The new features that are not available to TDS 4.2 clients include:

• char, varchar, nchar, nvarchar, binary, and varbinary values longer than 255 bytes are truncated to 255 bytes.
• TDS 4.2 does not support Unicode. nchar and nvarchar values are converted to char and varchar using the non-Unicode Windows® code page of the server, with possible loss of extended characters. ntext values cannot be retrieved.
• uniqueidentifer data types are converted to varbinary(16).
• NULL values in bit columns are returned as 0. Catalog and metadata functions report all bit columns as NOT NULL because NULL was not allowed for bit columns in version 6.5 and earlier.
• Catalog and metadata functions do not report the new SQL Server 7.0 data types (nchar, nvarchar, ntext, or uniqueidentifier).
• Prior to SQL Server 7.0, sysname was defined as varchar(30). In SQL Server 7.0, sysname is defined as nvarchar(128) to allow for longer identifiers that contain more extended characters. TDS 4.2 clients cannot access SQL Server 7.0 objects that have names more than 30 characters in length or that include characters not represented in the Windows code page on the client computer.

If any of these features are introduced into a SQL Server database, applications running with earlier versions of the SQL Server client software must be upgraded before they can access these new features.

The DB-Library for C API has not been upgraded for SQL Server 7.0. DB-Library applications still use TDS 4.2 to communicate with SQL Server 7.0, and are subject to the restrictions in this list. The Embedded SQL for C API is layered over DB-Library; it also operates as a TDS 4.2 client and is subject to the restrictions in this list.

The restrictions in this list apply to these clients:

• Any client using a 2.5 or 2.65 version of the SQL Server ODBC driver
• All DB-Library clients, regardless of version
• All Embedded SQL for C clients, regardless of version

All released versions of the Microsoft OLE DB Provider for SQL Server use TDS 7.0 and are not subject to the restrictions in this list.