sql - Case 表达式，如何从 Then 子句中的列中获取值

Question

如果以下条件为真，我需要从 Mortgage_Type 列中获取 THEN 的值。

1. Mortgage_Type 和 Category 是同一个表，Equipment 来自另一个表。

Tables are joining using Item_No. I need to find the Mortgage_Type of each item. I have 20+ Mortgage_Types if Category is main and Equipment is null then should display relevant Mortgage_Type

 when SUM (Mortgage_Type)is not null and SUM (Equipment)is null and
    sum(Category) ='M' THEN “value from Mortgage_Type column”

Answer 1

只需给出列名:

CASE 
   WHEN (Mortgage_Type)is not null and (Equipment)is null and (Category) ='M' 
    THEN Mortgage_Type
    ELSE <other value>
END