ORDER BY upper(...) 与 UNION 给我带来问题答案

【问题标题】：ORDER BY upper(...) with a UNION giving me problemsORDER BY upper(...) 与 UNION 给我带来问题
【发布时间】：2014-08-03 05:47:48
【问题描述】：

我很难弄清楚为什么会出现这个问题。

这段代码完全按照它应该的方式工作。它结合了两个表（MESSAGES 和 MESSAGES_ARCHIVE）并正确排序。

SELECT * FROM ( 
    SELECT rownum as rn, a.* FROM ( 
        SELECT  
        outbound.FROM_ADDR, outbound.TO_ADDR, outbound.EMAIL_SUBJECT

        from MESSAGES outbound 
        where (1 = 1) 

        UNION ALL

        SELECT  
        outboundarch.FROM_ADDR, outboundarch.TO_ADDR, outboundarch.EMAIL_SUBJECT

        from MESSAGES_ARCHIVE outboundarch 
        where (1 = 1)  

        order by FROM_ADDR DESC 
    ) a 
) where rn between 1 and 25

但是，此代码不起作用。

SELECT * FROM ( 
    SELECT rownum as rn, a.* FROM ( 
        SELECT  
        outbound.FROM_ADDR, outbound.TO_ADDR, outbound.EMAIL_SUBJECT

        from MESSAGES outbound 
        where (1 = 1) 

        UNION ALL

        SELECT  
        outboundarch.FROM_ADDR, outboundarch.TO_ADDR, outboundarch.EMAIL_SUBJECT

        from MESSAGES_ARCHIVE outboundarch 
        where (1 = 1)  

        order by upper(FROM_ADDR) DESC 
    ) a 
) where rn between 1 and 25

并返回此错误

ORA-01785: ORDER BY item must be the number of a SELECT-list expression
01785. 00000 -  "ORDER BY item must be the number of a SELECT-list expression"

我试图让这两个表排序，无论字母大小写如何，这就是我使用upper(FROM_ADDR) 的原因。有什么建议？谢谢！

【问题讨论】：

使用 UNIONS(ALL) 和 DISTINCT 时，ORDER by 应使用精确选择的表达式指定或提及为 1,2.. 作为列位置。一般来说，我会相信，按不在 SELECT 中的东西排序，oracle 隐含地包含在 select 中并对其进行排序。在这种情况下，oracle 可以 not 隐含地添加 UPPER() 只是 bevauce，它必须进行 SET 操作。

标签： sql oracle sql-order-by oracle-sqldeveloper union-all

【解决方案1】：

您的 upper() 返回一个值，但不是列名。而不是：

order by upper(FROM_ADDR) DESC

尝试：

order by upper(FROM_ADDR) as FROM_ADDR DESC

【讨论】：

【解决方案2】：

我不太清楚为什么会产生错误，但它可能与union 查询的范围规则有关。有一个简单的解决方法，使用row_number()：

SELECT * FROM ( 
    SELECT row_number() over (order by upper(FROM_ADDR)) as rn, a.*
    FROM ( 
        SELECT  
        outbound.FROM_ADDR, outbound.TO_ADDR, outbound.EMAIL_SUBJECT

        from MESSAGES outbound 
        where (1 = 1) 

        UNION ALL

        SELECT  
        outboundarch.FROM_ADDR, outboundarch.TO_ADDR, outboundarch.EMAIL_SUBJECT

        from MESSAGES_ARCHIVE outboundarch 
        where (1 = 1)  

    ) a 
)
where rn between 1 and 25

【讨论】：