在连续段上连接两个表

问题描述

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

表 T：

| 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（实际上是更多的列）：

| 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 和 fid 存在于每个表中，用于在 (tid,sid,ron) 形成的组内提供排序，这就是我想要维护的排序。

我怎样才能从这两个表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一个等级并将其用于 LEFT JOIN 内部的匹配，因为有些情况下匹配不是从组的末尾开始（例如 { {1}}）。另外，由于同一组中的tid=7可能有重复的值，我也不能盲目匹配，因为那样可能会炸毁行数。

解决方法

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),'x3',20,4),(3,'x5',5),(4,'c','x9',7),8),10),11),(6,'x11',22,12),(7,'x12',14),'x13',16),17),'x14',19)
          ) AS c(tid,sid,ron,val,seq)
   ),table_t_ranked AS (
       SELECT *,DENSE_RANK() OVER (PARTITION BY tid,ron ORDER BY seq ASC) AS ranking
       FROM table_t
   ),table_c AS (
           SELECT *
           FROM (VALUES
            (2,54),15),20),112),113)
           ) AS c(tid,fid)
   ),table_c_ranked AS (
       SELECT *,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,fid,seq
FROM foo       
WHERE ranking = ranking_t
ORDER BY tid,seq