Hi,
here is cut of one of our premium patches... It's without data backing up, but it's designed only for this type of conversion...
DB::Execute('UPDATE premium_schoolregister_lesson_field SET type=%s WHERE field=%s', array('multiselect','Teacher'));
PatchDBRenameColumn('premium_schoolregister_lesson_data_1','f_teacher','f_teacher','X');
DB::Execute('UPDATE premium_schoolregister_lesson_data_1 SET f_teacher='.DB::Concat(DB::qstr('__'),'f_teacher',DB::qstr('__')).' WHERE f_teacher is NOT NULL');
Paul