sql - ORDER BY upper(...) 和 UNION 给我带来了问题

Question

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。它组合了两个表(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，这段代码不起作用。

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。有什么建议么？谢谢!

Answer 1

我不太确定为什么会产生错误，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