getting one to one result from one to many relationship

Question

Hi there , my situation is that i have one to many relation ,like order and orderdetails ,i need to get order which has single order details.

Answer 1

How about:

select * 
from order
where order_number in
    (select order_number
     from order_details
     group by order_number
     having count(*) = 1)

Answer 2

Select o.*
from order o inner join order_detail d on o.id = d.order_id
group by o.*
having count(1) = 1

Answer 3

SELECT O1.order_number
  FROM Orders AS O1
 WHERE 1 = (
            SELECT COUNT(*)
              FROM OrderDetails AS D1
             WHERE O1.order_number = D1.order_number
           );