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我想连接两个表，其中第一个表的条目比第二个多，这样每个表的行都按顺序连接。也许一个小例子会有所帮助：

药片：

| tid | sid | ron | val | seqno |
| --- | --- | --- | --- | ---   |
| 1   | a   | x1  | 15  | 1     |
| 2   | b   | x2  | 10  | 3     |
| 2   | b   | x3  | 20  | 4     |
| 3   | a   | x5  | 10  | 5     |
| 4   | c   | x9  | 15  | 7     |
| 4   | c   | x9  | 15  | 8     |
| 4   | c   | x9  | 20  | 10    |
| 4   | c   | x9  | 15  | 11    |
| 6   | b   | x11 | 22  | 12    |
| 7   | b   | x12 | 10  | 14    |
| 7   | b   | x13 | 10  | 16    |
| 7   | b   | x13 | 10  | 17    |
| 7   | b   | x14 | 10  | 19    |

第二个表（表C）如下（实际上，更多列）：

| tid | sid | ron | val | fid |
| --- | --- | --- | --- | --- |
| 2   | b   | x3  | 20  | 54  |
| 4   | c   | x9  | 15  | 12  |
| 4   | c   | x9  | 15  | 14  |
| 4   | c   | x9  | 20  | 15  |
| 4   | c   | x9  | 15  | 20  |
| 7   | b   | x13 | 10  | 112 |
| 7   | b   | x13 | 10  | 113 |

seqNo并fid在每个表中提供由 组成的组内的排序(tid, sid, ron)，这就是我想要维护的排序。

我怎样才能从这两个表中得到类似于下表的内容？

| tid | sid | ron | val | fid | seqno |
| --- | --- | --- | --- | --- | ---   | 
| 2   | b   | x3  | 20  | 54  | 4     |
| 4   | c   | x9  | 15  | 12  | 7     |
| 4   | c   | x9  | 15  | 14  | 8     |
| 4   | c   | x9  | 20  | 15  | 10    |
| 4   | c   | x9  | 15  | 20  | 11    |
| 7   | b   | x13 | 10  | 112 | 16    |
| 7   | b   | x13 | 10  | 113 | 17    |

我无法为组中的每个元素分配等级并将其用于匹配内部 a LEFT JOIN，因为在某些情况下匹配不是从组的末尾开始（例如tid=7）。另外，因为val在同一个组中可能有重复的值，我也不能盲目地匹配它，因为这可能会炸毁行数。

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1 回答 1

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这是我昨晚设法得到的，似乎工作正常：

WITH
  table_t AS (
          SELECT *
          FROM (VALUES
            (1,'a','x1',15,1),
            (2,'b','x2',10,3),
            (2,'b','x3',20,4),
            (3,'a','x5',10,5),
            (4,'c','x9',15,7),
            (4,'c','x9',15,8),
            (4,'c','x9',20,10),
            (4,'c','x9',15,11),
            (6,'b','x11',22,12),
            (7,'b','x12',10,14),
            (7,'b','x13',10,16),
            (7,'b','x13',10,17),
            (7,'b','x14',10,19)
          ) AS c(tid, sid, ron, val, seq)
   ),
   table_t_ranked AS (
       SELECT *
       , DENSE_RANK() OVER (PARTITION BY tid, sid, ron ORDER BY seq ASC) AS ranking
       FROM table_t
   ),
   table_c AS (
           SELECT *
           FROM (VALUES
            (2,'b','x3',20,54),
            (4,'c','x9',15,12),
            (4,'c','x9',15,14),
            (4,'c','x9',20,15),
            (4,'c','x9',15,20),
            (7,'b','x13',10,112),
            (7,'b','x13',10,113)
           ) AS c(tid, sid, ron, val, fid)
   ),
    table_c_ranked AS (
       SELECT *
       , DENSE_RANK() OVER (PARTITION BY tid, sid, ron ORDER BY fid ASC) AS ranking
       FROM table_c
   ),
   foo AS (
       SELECT c.*
        , t.seq
        , t.ranking as ranking_t
        FROM table_c_ranked c
        LEFT JOIN table_t_ranked t
        ON c.tid = t.tid
        AND c.sid = t.sid
        AND c.ron = t.ron
        AND c.val = t.val
   )

SELECT tid, sid, ron, val, fid, seq
FROM foo       
WHERE ranking = ranking_t
ORDER BY tid, seq
于 2021-07-22T06:47:10.847 回答