SQL Server：有关数据返回的问题

Question

As a novice SQL Server user, I ran into a problem that I did not know a solution to. I am trying to draw a master list of items and their cost. Some items have component items with their own cost, and those need to be called as well. However, whenever I try to include the component items, the query does not return items without components.

For example: I call 3 items from the query: A, B, and C. It displays their costs perfectly. However, I learn that Item C has a Component Item X. When I try to add a column for component item and it's cost, Items A and B are not returned in the query as they do not have a component item. I can't figure out why a NULL isn't placed when an item does not have a component item to accompany it.

Here is my query:

SELECT 
    T1.item_no, T2.item_cost, T1.component_item_no, T2.item_cost(2)
FROM 
    T1 
INNER JOIN 
    T2 ON T2.item_no = T1.item_no
INNER JOIN 
    T2(2) ON T2.item_no = T1.component_item_no  

I had to call T2 twice so I could call item cost for both the top level item as well as it's component.

Sample return data:

Answer 1

将组件项目表的INNER JOIN更改为LEFT JOIN