Question

我想得到一个表有两列和多行的答案。对于每一行，我希望以某种顺序显示两列，例如：

初始表：

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

The target table is:

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

如何解决？谢谢！

Answer 1

你可以尝试

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

与Marco相似，但使用greatest和least函数：

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

Answer 3

如果我理解你的问题，那么以下更新应该交换名称B'低于'名称A的名称。

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

Answer 4

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

如何在元组内排序（SQL）

4 个答案: