Question

我试图通过以下规则获取客户的地址：

获取首选地址（preferred_ind =＆＃39; Y＆＃39;）
如果是多个首选地址，请先获得一个（max（address_id）正常）
如果没有首选地址，那么只需获得第一个（max（address_id）就可以了。）
如果没有地址，只需返回没有地址信息的客户名称。

preferred_ind可以是＆＃39; Y＆＃39;，＆＃39; N＆＃39;或null。

SELECT c.first_name,
       c.last_name,
       a.address_line_1,
       a.city,
       a.state_code,
       a.postal_code
FROM my_customer c,
     my_customer_address a
WHERE c.customer_id = a.customer_id(+)
AND (a.address_id IS NULL OR a.address_id = (SELECT MAX(a2.address_id)
                                             FROM my_customer_address a2
                                             WHERE a2.customer_id = c.customer_id
                                             ORDER BY nvl(a2.preferred_ind, 'N') DESC));

但是，当然，Oracle不允许在子查询中使用ORDER BY。那么我怎样才能得到我想要的结果呢？

感谢。

Answer 1

您应该重写为ANSI Outer Join语法并应用ROW_NUMBER：

--untested
SELECT c.first_name,
       c.last_name,
       a.address_line_1,
       a.city,
       a.state_code,
       a.postal_code
FROM my_customer c
LEFT JOIN 
 (
   SELECT customer_id,
       address_line_1,
       city,
       state_code,
       postal_code,
       ROW_NUMBER() 
       OVER (PARTITION BY customer_id
             ORDER BY preferred_ind = 'Y' DESC, address_id DESC) AS rn
   FROM my_customer_address
 ) a
ON c.customer_id = a.customer_id
AND a.rn = 1

oracle子查询在where子句中有order by

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