枚举内部联接中的行 [英] Enumerating rows in a inner join

问题描述

我的桌子

id name num
1  a    3
2  b    4

我需要返回每行num次.我是这样的.

I need to return every row num number of times. I do it this way.

  select DB.BAN_KEY as BAN_KEY, DB.CUST_FULLNAME as CUST_FULLNAME
  from TST_DIM_BAN_SELECTED DB
  inner join (select rownum rn from dual connect by level < 10) a
  on a.rn <= DB.N

结果表如下所示.

id  name
1   a
1   a
1   a
2   b
2   b
2   b
2   b

但是我还需要将组中的每一行都这样编号.

But I also need every row in the group to be numbered like this.

id  name row_num
1   a    1
1   a    2
1   a    3
2   b    1
2   b    2
2   b    3
2   b    4

我该怎么办?

推荐答案

您不需要内部连接到虚拟表或使用解析函数来生成行号；您可以只在表本身上使用connect by(及其对应的level函数)，就像这样:

You don't need an inner join to a dummy table or an analytic function to generate the row numbers; you could just use connect by (and its corresponding level function) on the table itself, like so:

WITH tst_dim_ban_selected AS (SELECT 1 ban_key, 'a' cust_fullname, 3 n FROM dual UNION ALL
                              SELECT 2 ban_key, 'b' cust_fullname, 4 n FROM dual)
-- end of mimicking your table with data in it. See SQL below
SELECT db.ban_key,
       db.cust_fullname,
       LEVEL row_num
FROM   tst_dim_ban_selected db
CONNECT BY LEVEL <= db.n
           AND PRIOR db.ban_key = db.ban_key -- assuming this is the primary key
           AND PRIOR sys_guid() IS NOT NULL;

   BAN_KEY CUST_FULLNAME    ROW_NUM
---------- ------------- ----------
         1 a                      1
         1 a                      2
         1 a                      3
         2 b                      1
         2 b                      2
         2 b                      3
         2 b                      4

如果表的主键中除ban_key之外还有其他列，则需要确保它们包含在prior <column> = <column> s的connect by子句列表中.因此，connect by可以唯一地标识每一行，这意味着它仅在该行上循环，而在其他行上则没有. PRIOR sys_guid() IS NOT NULL是必需的，以防止发生by by循环.

If you have other columns than ban_key in the table's primary key, you need to make sure they are included in the connect by clause's list of prior <column> = <column>s. This is so the connect by can identify each row uniquely, meaning that it's looping just over that row and no others. The PRIOR sys_guid() IS NOT NULL is required to prevent connect by loops from occurring.

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