Question

I have 2 tables (Orders, OrderItems) that are related based on a column OrderID. I need to find all Orders that do not have any OrderItems.

Answer 1

We use JOIN to find related data. To find data without any related data, we can use an anti-join.

The following joins the tables, then selects those without any order items. This tends to be more efficient that a WHERE id NOT IN (...) style query.

select *
from
    Orders O
    left outer join OrderItems I
    on I.OrderId = O.Id
where
    I.Id is null