I would say that's the incorrect query, since you're saying I want (I assume you're searching on the Category table), all categories with FatherID that are either 275 or 44 AND CategoryID that's 163. I'm guessing you're wanting to do either. In that case, you need a GT::SQL::Condition object to do what you want. Something like:

$DB->table('Category', 'Links', 'CatLinks')->select(GT::SQL::Condition->new(FatherID => 'IN' => [275, 44], CategoryID => '=' => 163, 'OR'), VIEWABLE);

That makes it an OR condition between the two FatherID and CategoryID constraints, and we want to use the VIEWABLE constant instead of just checking for isValidated because that takes payments into consideration as well (if enabled).

Adrian