如何从条件中的两个不同列中进行选择并从SQL中连接它们

Question

我希望加入两个专栏......这是一个想法......

=======================================================
    id  | firstname  |        lastname
=======================================================
    1   | Peter      | Das
-------------------------------------------------------
    2   | Das        | James
-------------------------------------------------------
    3   | vector     | Call
______________________________________________________________
    4   | cans       | Das

sql查询应该看起来像这样(伪代码)

SELECT (lastname WHERE firstname='Das' AND firstname WHERE lastname='Das' 
    ORDER BY ID DESC) AS name

结果集看起来应该是这样的

    ======================
        name
    ======================
        cans
    ---------------------------------------
        James
    ---------------------------------------
        Peter

现在任何人都可以告诉我什么是确切的查询

每个想法提示建议都是受欢迎的

Answer 1

  SELECT CASE
             WHEN firstname = 'Das' THEN lastname
             ELSE firstname
         END AS name
    FROM table
   WHERE firstname = 'Das'
      OR lastname = 'Das'
ORDER BY id DESC