如何在一個元組內排序（SQL）

Question

我想得到一個答案，表中有兩列和多行。對於每一行，我想以某種順序顯示兩個列，例如：

初始表：

+-----------+---------+ 
| nameA  | nameB | 
+-----------+---------+ 
| Ca  | Us  | 
| Db  | Ac  | 
+-----------+---------+ 

The target table is: 

+-----------+---------+ 
| nameA  | nameB | 
+-----------+---------+ 
| Ca  | Us  | 
| Ac  | Db  | 
+-----------+---------+ 

如何解決呢？謝謝！

Answer 1

你可以嘗試

SELECT 
    (CASE WHEN nameA <= nameB THEN nameA 
    ELSE nameB END) AS field1, 
    (CASE WHEN nameA < nameB THEN nameB 
    ELSE nameA END) AS field2 
FROM your_table 

Answer 2

如果我正確理解你的問題，那麼下面的更新應該換地方名B是名A.「低於」的名字

UPDATE table 
SET nameA = nameB, nameB = nameA 
WHERE nameB < nameA; 

Answer 3

馬可波羅的類似，但使用greatest和least功能：

SELECT 
    least(nameA,nameB) AS field1, 
    greatest(nameA,nameB) AS field2 
FROM your_table 

Answer 4

SELECT nameA, nameB 
    FROM YourTable 
WHERE nameA <= nameB 
UNION 
SELECT nameB AS nameA, nameA AS nameB 
    FROM YourTable 
WHERE nameB < nameA;