Database buckle force customers to order and never question

 

 Analysis: The title is given in two tables can be drawn should be left connected to the query connection. Usually by the condition never anything the user should be drawn with a null operators, testing whether the field is null.

答案：select Name as Customers from Customers left join Orders on Customers.Id=Orders.CustomerId where Orders.CustomerId is null

Knowledge Point: null operator to test whether the field is null, comparison operators only apply to conditional expressions.