如何将 rank() 与内部连接一起使用？

Posted 2023-03-29

【中文标题】如何将 rank() 与内部连接一起使用？

【英文标题】：How do I use rank() with an inner join?

【发布时间】：2012-04-03 20:35:32

【问题描述】：

我想将我的 CHEESE 表与 FRESHNESS 连接起来以获取 CHEESE 和 FRESHNESS 代码 每个奶酪 ID 的 max(seq_no) 为 MOLD 的奶酪。

使用 rank() 时，我在哪里加入 FRESHNESS？

CHEESE                                    FRESHNESS
CHEESE_ID  SEQ_NO  FRESH_CODE             FRESH_CODE   FRESH_DESC      
=================================         ========================
  1         1        MOLD                 MOLD         MOLDY CHEESE    
  1        23        FRSH                 FRSH         EDIBLE
  1        34        FRSH
  2         2        FRSH
  2        18        MOLD
  3         3        MOLD
  3         5        MOLD
  3         7        MOLD


 DESIRED RESULT
 ==========================
 CHEESE_ID  SEQ_NO  FRESH_CODE  FRESH_DESC      SEQ_RANK
 2           18     MOLD        MOLDY CHEESE    1
 3            7     MOLD        MOLDY CHEESE    1

这是我用来获取所需序列号的代码。

select 
       cheese_id,seq_no,fresh_code,seq_rank
  from ( select 
         cheese_id,seq_no, fresh_code, 
         rank() over (partition by cheese_id
                          order by seq_no desc) seq_rank
from cheese
where seq_rank = 1
 and  fresh_code = 'MOLD'

【参考方案1】：

您可以在子查询中进行连接

select cheese_id,seq_no,fresh_code,fresh_desc,seq_rank
  from ( select cheese_id,
                seq_no, 
                fresh_code, 
                fresh_desc,
                rank() over (partition by cheese_id
                                 order by seq_no desc) seq_rank
          from cheese
               join freshness using (fresh_code) )
 where seq_rank = 1
   and fresh_code = 'MOLD'

或者你可以加入你的子查询

select cheese_id,seq_no,fresh_code,fresh_desc,seq_rank
  from ( select cheese_id,
                seq_no, 
                fresh_code, 
                fresh_desc,
                rank() over (partition by cheese_id
                                 order by seq_no desc) seq_rank
          from cheese ) cheese_outer
       join freshness using (fresh_code)
 where seq_rank = 1
   and fresh_code = 'MOLD'