在无序的行集上选择下一行或上一行

Question

我有一个UNION SQL查询可以生成无序的一组行。结果与

 
+----+----------------------+-------+ 
| id | name     | value | 
+----+----------------------+-------+ 
| 3 | John     | 21 | 
+----+----------------------+-------+ 
| 2 | Jim     | 5  | 
+----+----------------------+-------+ 
| 4 | Adrian    | 25 | 
+----+----------------------+-------+ 
| 1 | Sam     | 22 | 
+----+----------------------+-------+ 

相同如果选择第二行，如何选择下一行或上一行？

Answer 1

提供在MySQL中失踪rownum功能常见的伎俩：

SELECT 
    @rownum:=@rownum+1 AS rownum, 
    id, name, value 
FROM 
    (
     (SELECT id, name, value FROM buyers ORDER BY id) 
     UNION 
     (SELECT id, name, value FROM seller ORDER BY id) 
    ) subq, 
    (SELECT @rownum:=0) r; 

然后使用rownum场行之间进行导航。