Question

I’m trying to get data from another database using the OPENDATASOURCE command, but I get an error about DisallowAdHocAccess.

The SQL Server version is 2008 Express Edition, running on a remote site.

Answer 1

OPENROWSET can be used to access remote data from OLE DB data sources
only if the DisallowAdhocAccess registry option is explicitly set to
0. When this option is not set, the default behavior does not allow ad
hoc access.

HOW TO: Use the DisallowAdHocAccess Setting to Control Access to Linked Servers

Accessing External Data

An ad hoc name is used for infrequent queries against OLE DB data
sources that are not defined as linked servers. In SQL Server, the
OPENROWSET and OPENDATASOURCE functions provide connection information
for accessing data from OLE DB data sources. By default, ad hoc
names are not supported. The DisallowAdhocAccess provider option must
be set to 0 and the Ad Hoc Distributed Queries advanced configuration
option must be enabled.

Security Note

Enabling the use of ad hoc names means that any authenticated login to
SQL Server can access the provider. SQL Server administrators should
enable this feature only for highly trusted providers that are safe to
be accessed by any local login.

OPENROWSET and OPENDATASOURCE should be used only to reference OLE DB
data sources that are accessed infrequently. For any data sources that
will be accessed more than several times, define a linked server.
Neither OPENDATASOURCE nor OPENROWSET provide all the functionality of
linked server definitions. This includes security management and the
ability to query catalog information. Every time that these functions
are called, all connection information, including passwords, must be
provided.