Question

我有一张桌子：

+-------+-------+----------+
| GROUP | State | Priority |
+-------+-------+----------+
|   1   |  MI   |     1    |
|   1   |  IA   |     2    |
|   1   |  CA   |     3    |
|   1   |  ND   |     4    |
|   1   |  AZ   |     5    |
|   2   |  IA   |     2    |
|   2   |  NJ   |     1    |
|   2   |  NH   |     3    |

And so on...

如何编写一个查询，使所有状态组按组按优先级顺序排列？像这样：

+-------+--------------------+
| GROUP |        SET         |
+-------+--------------------+
|   1   | MI                 |
|   1   | MI, IA             |
|   1   | MI, IA, CA         |
|   1   | MI, IA, CA, ND     |
|   1   | MI, IA, CA, ND, AZ |
|   2   | NJ                 |
|   2   | NJ, IA             |
|   2   | NJ, IA, NH         |
+-------+--------------------+

这类似于我的问题here，我尝试修改该解决方案，但是，我只是一个40瓦的灯泡，这是一个60瓦的问题...

Answer 1

这个问题实际上比您链接的问题的答案简单，这是解决该问题的绝佳方法。但是，它使用相同的层次查询，connect by

如果priority始终是连续的数字序列，则可以使用

SELECT t.grp, level, ltrim(SYS_CONNECT_BY_PATH(state,','),',')   as "set"  
   from  t 
   start with priority = 1
 connect by   priority = prior priority + 1
            and grp = prior grp

但是，如果并非总是如此，我们将要求row_number()根据优先级顺序（不必是连续的整数）来定义序列

with t2 AS
( 
  select t.*, row_number() 
        over ( partition by grp order by priority) as rn from t
)
SELECT t2.grp, ltrim(SYS_CONNECT_BY_PATH(state,','),',')   as "set"
   from  t2 
   start with priority = 1
 connect by   rn = prior rn + 1
            and grp = prior grp

DEMO

Answer 2

我意识到这已经得到了回答，但是我想看看是否可以使用ANSI标准语法来做到这一点。 “ connect by”是仅Oracle的一项功能，以下将在多个数据库上运行：

WITH
    -- ASET is just setting up the sample dataset
    aset AS
        (SELECT 1 AS grp, 'MI' AS state, 1 AS priority FROM DUAL
         UNION ALL
         SELECT 1 AS grp, 'IA', 2 FROM DUAL
         UNION ALL
         SELECT 1 AS grp, 'CA', 3 FROM DUAL
         UNION ALL
         SELECT 1 AS grp, 'ND', 4 FROM DUAL
         UNION ALL
         SELECT 1 AS grp, 'AZ', 5 FROM DUAL
         UNION ALL
         SELECT 2 AS grp, 'IA', 2 FROM DUAL
         UNION ALL
         SELECT 2 AS grp, 'NJ', 1 FROM DUAL
         UNION ALL
         SELECT 2 AS grp, 'NH', 3 FROM DUAL),
    bset AS
        -- In BSET we convert the ASET records into comma separated values
        (  SELECT grp, LISTAGG( state, ',' ) WITHIN GROUP (ORDER BY priority) AS set1
             FROM aset
         GROUP BY grp),
    cset ( grp
         , set1
         , set2
         , pos ) AS
        -- CSET breaks our comma separated values up into multiple rows
        -- Each row adding the next CSV value
        (SELECT grp                                                         AS grp
              , set1                                                        AS set1
              , SUBSTR( set1 || ',', 1, INSTR( set1 || ',', ',' ) - 1 )     AS set2
              , 1                                                           AS pos
           FROM bset
         UNION ALL
         SELECT grp              AS grp
              , set1             AS set1
              , SUBSTR( set1 || ','
                      , 1
                      ,   INSTR( set1 || ','
                               , ','
                               , 1
                               , pos + 1 )
                        - 1 )    AS set2
              , pos + 1          AS pos
           FROM cset
          WHERE INSTR( set1 || ','
                     , ','
                     , 1
                     , pos + 1 ) > 0)
  SELECT grp, set2
    FROM cset
ORDER BY grp, pos;

来自单个表的集合，按列分组

2 个答案: