Choosing a TDS protocol version

The TDS protocol version is probably something you'd rather not know even existed, much less something you'd have to choose. But there's not that much to it, really. Unless you run into an incompatibility, you're best off running with the highest protocol version supported by your server. That's what the vendors' own products do, which is why when you read the Sybase or Microsoft documentation you find no mention of TDS versions.

TipAvoid obsolete versions.
 

In former versions of Microsoft SQL Server protocol 7.1 was referred as 8.0 while 7.2 was referred as 9.0.

For compatibility reasons version 8.0 is still handled by FreeTDS but you should avoid to use it as it could be removed in a future version or it could clash with a future SQL server version.

Table 3-1. Versions of the TDS Protocol, by Product

ProductTDS VersionComment
Sybase before System 10, Microsoft SQL Server 6.x4.2Still works with all products, subject to its limitations.
Sybase System 10 and above5.0Still the most current protocol used by Sybase.
Sybase System SQL Anywhere5.0 only Originally Watcom SQL Server, a completely separate codebase. Our best information is that SQL Anywhere first supported TDS in version 5.5.03 using the OpenServer Gateway (OSG), and native TDS 5.0 support arrived with version 6.0.
Microsoft SQL Server 7.07.0Includes support for the extended datatypes in SQL Server 7.0 (such as char/varchar fields of more than 255 characters), and support for Unicode.
Microsoft SQL Server 20007.1Include support for bigint (64 bit integers), variant and collation on all fields. Collation is not widely used.
Microsoft SQL Server 20057.2Includes support for varchar(max), varbinary(max), xml datatypes and MARS[a].
Microsoft SQL Server 20087.3Includes support for time, date, datetime2, datetimeoffset.
Notes:
a. Multiple Active Result Sets.

For best results, use the highest version of the protocol supported by your server. If you encounter problems, try a lower version. If that works, though, please report it to the mailing list! [1]

TDS 4.2 has limitations

The protocol version may also affect how database servers interpret commands. For example, Microsoft SQL Server 2000 is known to behave differently with versions 4.2 and 7.0. Version 7.0 is recommended for compatibility with SQL Server tools.

Notes

[1]

Want to help? Try out the auto-protocol feature. FreeTDS has experimental support for iteratively trying protocol connections until it finds one the server accepts. This is suitable when query responses are non-trivial (because the tiny delay in connecting is thus insignificant). Try setting your TDS version to 0 and report your results.