选择不同和内部加入图像数据类型

Question

我试图选择所有已下定单的唯一客户，但是当我尝试包含照片时出现错误。

Order Table 
ID  | CustomerID 
----------------------- 
1  | 2 
2  | 1 
3  | 2 


Customer Table 
ID  | Name | Photo (image, null) 
-------------------------- 
1  | John | image 
2  | Adam | image 
3  | Jack | image 


Expected result 
    CustomerID | Name | Photo 
-------------------------------- 
1    | John | image 
2    | Adam | image 

而且我的查询到目前为止：

SELECT Distinct o.CustomerID, c.Name, c.Photo 
FROM Order o 
inner join Customer c on o.CustomerID = o.ID 

这提供了以下错误：

The image data type cannot be selected as DISTINCT because it is not comparable.

Answer 1

查询应该是

select * from customers where id in (select customerID from orders)