如何在Oracle10g中按顺序连接多行

Question

如果我有这样的数据:

GROUP  |  SEQUENCE  |  COMMAND
------------------------------
ONE    |     3      |  <message2>MESSAGE</message2>
ONE    |     1      |  <?xml version="1.0" encoding="UTF-8"?>
ONE    |     2      |  <message1>MESSAGE</message1>
TWO    |     2      |  <message2>MESSAGE</message2>
TWO    |     1      |  <?xml version="1.0" encoding="UTF-8"?>
........
TWO    |    10      |  <message9>MESSAGE</message9>

如何将命令连接成这样:

GROUP  |  COMMAND
-----------------
ONE    |  <?xml version="1.0" encoding="UTF-8"?>,<message1>MESSAGE</message1>,<message2>MESSAGE</message2>
TWO    |  <?xml version="1.0" encoding="UTF-8"?>,<message1>MESSAGE</message1>, .. ,<message9>MESSAGE</message9>

我在下面使用了这个查询，但是命令列不是按照它们的序列号排列的:

SELECT GROUP, WM_CONCAT(COMMAND) AS COMMAND
     FROM (SELECT GROUP, SEQUENCE, COMMAND FROM TBL ORDER BY SEQUENCE)
     GROUP BY GROUP
//AND THIS
SELECT GROUP, WM_CONCAT(DISTINCT COMMAND) AS COMMAND
 FROM (SELECT GROUP, SEQUENCE, COMMAND FROM TBL ORDER BY SEQUENCE)
 GROUP BY GROUP

如有任何意见和建议，我将不胜感激。^ _ ^

Answer 1

不要使用WM_CONCAT。为什么不在Oracle中使用WM_CONCAT函数?

参见此主题https://stackoverflow.com/a/28758117/3989608。

它是未记录的，并且任何依赖于WM_CONCAT的应用程序一旦升级到12c将无法工作，因为它已从最新的12c版本中删除。

字符串聚合有多种方法，具体取决于数据库版本。请看下面的几个例子: 11 gr2

使用LIASTAGG:

SQL> SELECT grp,
  2    listagg(command, ',') WITHIN GROUP(
  3  ORDER BY seq) command
  4  FROM t
  5  GROUP BY grp;
GRP COMMAND
--- --------------------------------------------------------------------------------------------
ONE <?xml version=1.0 encoding=UTF-8?>,<message1>MESSAGE</message1>,<message2>MESSAGE</message2>
TWO <?xml version=1.0 encoding=UTF-8?>,<message2>MESSAGE</message2>,<message9>MESSAGE</message9>
SQL>

使用ROW_NUMBER()和SYS_CONNECT_BY_PATH:

SQL> SELECT grp,
  2         LTRIM(MAX(SYS_CONNECT_BY_PATH(command,','))
  3         KEEP (DENSE_RANK LAST ORDER BY seq),',') command
  4  FROM   (SELECT grp,
  5                 command,
  6                 seq,
  7                 ROW_NUMBER() OVER (PARTITION BY grp ORDER BY seq) AS curr,
  8                 ROW_NUMBER() OVER (PARTITION BY grp ORDER BY seq) -1 AS prev
  9          FROM   t)
 10  GROUP BY grp
 11  CONNECT BY prev = PRIOR curr AND grp = PRIOR grp
 12  START WITH curr = 1;
GRP COMMAND
--- --------------------------------------------------------------------------------------------
ONE <?xml version=1.0 encoding=UTF-8?>,<message1>MESSAGE</message1>,<message2>MESSAGE</message2>
TWO <?xml version=1.0 encoding=UTF-8?>,<message2>MESSAGE</message2>,<message9>MESSAGE</message9>
SQL>