ORDER BY upper(...)与UNION给我带来问题

Question

我在弄清楚为什么遇到这个问题时遇到了一些麻烦.

此代码完全适用于它应该如何工作.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"

无论字母大小写,我都试图将这两张桌子排好,这就是我使用的原因upper(FROM_ADDR).有什么建议？谢谢!

Answer 1

我不太确定为什么会产生错误，但它可能与查询的范围规则有关union。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