Andreas,
Is this an action query (append, update, delete, make-table)? Are you
referring to the warning "you are about to append/delete modify etc"?
If yes, and you are running the query through a macro, precede the
OpenQuery action with a SetWarnings action, argument False; then
supersede it with another SetWarnings, argument True to restore warnings.
If you are running an action query in VBA code, like:
DoCmd.RunSQL strSQL
then change that to:
CurrentDb.Execute strSQL
HTH,
Nikos