[freetds] FreeTDS creating all fields as not null

Lowden, James K james.k.lowden at alliancebernstein.com
Thu Sep 21 14:07:27 EDT 2006

> From: Eloy Lafuente
> Sent: Thursday, September 21, 2006 12:37 PM
> I'm using FreeTDS to handle one MSSQL 2005 server
> ...
> Everytime I create one table having NULL fields, they become NOT
> NULL in the target DB.
> Curiously, executing the same CREATE TABLE statement from the "tsql"
> command line interface, the table is created properly (with NULL
> fields being NULL).

Whether a column in a CREATE TABLE statement is NULL or NOT NULL by
default (when not explicit in the DDL) depends on the connection options
(a/k/a session properties).  Cf. "dbcc useroptions".  Database options
also play a role, cf. sp_dboption.  In particular, see "When not
explicitly specified, column nullability follows these rules" in the
description of CREATE TABLE in books online.

ODBC connections are given different session properties at connect time
than are db-lib connections.  The FreeTDS db-lib turns off the "I'm an
ODBC driver" bit when it logs in, whereas tsql does not, so tsql's
behavior will differ in this regard from a db-lib application e.g.
bsqldb or the PHP mssql extension.  



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