如何從兩個不同勢列中選擇條件，從SQL

Question

加入他們

我期待加入兩列單...這裏有一個想法..

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

SQL查詢應該是這樣的（僞）

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

名稱和ResultSet應該是這樣的

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

現在誰能告訴我什麼是電子XACT查詢

每一個想法提示建議，歡迎

Answer 1

看起來像一個工作，一個UNION查詢

SELECT id, firstName AS name 
FROM table 
WHERE lastName = 'Das' 
UNION ALL 
SELECT id, lastName AS name 
FROM table 
WHERE firstName = 'Das' 
ORDER BY id DESC 

Answer 2

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

Answer 3

你沒告訴我們你的表的名稱。假設它被稱爲mynames，這應該工作：

select case when firstname = 'Das' then lastname 
else firstname end as name from mynames 
where lastname = 'Das' or firstname = 'Das' order by id desc; 

這裏是MySQL的一些測試代碼，我寫驗證解決方案的工作原理：

mysql> create table mynames(
    -> id int unsigned primary key auto_increment, 
    -> firstname varchar(32) not null, 
    -> lastname varchar(32) not null 
    ->) engine=innodb; 
Query OK, 0 rows affected (0.45 sec) 

mysql> insert into mynames (firstname, lastname) values 
    -> ('Peter', 'Das'), 
    -> ('Das', 'James'), 
    -> ('vector', 'Call'), 
    -> ('cans', 'Das'); 
Query OK, 4 rows affected (0.49 sec) 
Records: 4 Duplicates: 0 Warnings: 0 

mysql> select * from mynames; 
+----+-----------+----------+ 
| id | firstname | lastname | 
+----+-----------+----------+ 
| 1 | Peter  | Das  | 
| 2 | Das  | James | 
| 3 | vector | Call  | 
| 4 | cans  | Das  | 
+----+-----------+----------+ 
4 rows in set (0.00 sec) 

mysql> select case when firstname = 'Das' then lastname 
    -> else firstname end as name from mynames 
    -> where lastname = 'Das' or firstname = 'Das' order by id desc; 
+-------+ 
| name | 
+-------+ 
| cans | 
| James | 
| Peter | 
+-------+ 
3 rows in set (0.00 sec)