通常，WM_CONCAT 是一个聚合函数，它从用逗号分隔的表中返回值，就像这里一样。
假设我有一个foo这样的表：
col_id | col_text
111 | This
111 | is
111 | a
111 | test.
如果我使用这个查询：
SELECT CAST(WM_CONCAT(col_text) AS VARCHAR2(100)), col_id FROM foo
结果是
This, is, a, test.
是否可以将分隔符（','）更改为其他字符，如函数'.'或函数？'|'WM_CONCAT()
或者创建一个可以像这样执行的用户定义函数WM_CONCAT()？
You might want to use LISTAGG.
SELECT col_id,
LISTAGG(col_text, '|') WITHIN GROUP (ORDER BY col_text) text
FROM table1
GROUP BY col_id
Output:
| COL_ID | TEXT |
----------------------------
| 111 | This|a|is|test. |
UPDATE If you need to get distinct text values in a list
SELECT col_id,
LISTAGG(col_text, '|')
WITHIN GROUP (ORDER BY col_text) text
FROM
(
SELECT DISTINCT col_id, col_text
FROM table1
)
GROUP BY col_id
LISTAGG 的问题是它返回 varchar2 并且限制为 4000 字节
SELECT LISTAGG(LEVEL, CHR(10)) WITHIN GROUP (ORDER BY NULL)
FROM Dual
CONNECT BY LEVEL < 2000
ORA-01489 Result of string concat is too large
我找到了一种解决方法，但它看起来很难看，而且速度较慢
SELECT EXTRACT(XMLTYPE('<doc>' || XMLAGG(XMLTYPE('<ln>' || LEVEL || CHR(10) || '</ln>')).GetClobVal() || '</doc>'), '/doc/ln/text()').GetClobVal()
FROM Dual
CONNECT BY LEVEL < 2000
是否可以将分隔符（'，'）更改为其他字符，如'。' 或“|” WM_CONCAT() 函数？
请勿使用WM_CONCAT，因为它是一个未记录的功能，并且已从最新的12c 版本中删除。任何一直依赖wm_concat功能的应用程序一旦升级到12c. 请参阅为什么不在 Oracle 中使用 WM_CONCAT 函数？
SQL> select banner from v$version where rownum = 1;
BANNER
----------------------------------------------------------------------------
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
SQL> SELECT object_name
2 FROM dba_objects
3 WHERE owner='WMSYS'
4 AND object_name LIKE 'WM\_%' ESCAPE '\';
OBJECT_NAME
----------------------------------------------------------------------------
WM_REPLICATION_INFO
WM_RDIFF
WM_PERIOD
WM_PERIOD
WM_OVERLAPS
WM_MEETS
WM_LESSTHAN
WM_LDIFF
WM_INTERSECTION
WM_INSTALLATION
WM_GREATERTHAN
WM_EVENTS_INFO
WM_ERROR
WM_ERROR
WM_EQUALS
WM_DDL_UTIL
WM_DDL_UTIL
WM_CONTAINS
WM_COMPRESS_BATCH_SIZES
WM_COMPRESSIBLE_TABLES
20 rows selected.
您将收到“<strong>invalid identifier”错误：
SQL> SELECT banner FROM v$version;
BANNER
----------------------------------------------------------------------------
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
PL/SQL Release 12.1.0.1.0 - Production
CORE 12.1.0.1.0 Production
TNS for 64-bit Windows: Version 12.1.0.1.0 - Production
NLSRTL Version 12.1.0.1.0 - Production
SQL> SELECT deptno, wm_concat(ename) FROM emp;
SELECT deptno, wm_concat(ename) FROM emp
*
ERROR at line 1:
ORA-00904: "WM_CONCAT": invalid identifier
因此，没有必要依赖最新版本中不再提供的未记录功能。
有多种字符串聚合技术：
例如，
SELECT deptno, LISTAGG(ename, ',') WITHIN GROUP (ORDER BY ename) AS employees
FROM emp
GROUP BY deptno;
DEPTNO EMPLOYEES
---------- --------------------------------------------------
10 CLARK,KING,MILLER
20 ADAMS,FORD,JONES,SCOTT,SMITH
30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
3 rows selected.
例如，
SELECT deptno,
LTRIM(MAX(SYS_CONNECT_BY_PATH(ename,','))
KEEP (DENSE_RANK LAST ORDER BY curr),',') AS employees
FROM (SELECT deptno,
ename,
ROW_NUMBER() OVER (PARTITION BY deptno ORDER BY ename) AS curr,
ROW_NUMBER() OVER (PARTITION BY deptno ORDER BY ename) -1 AS prev
FROM emp)
GROUP BY deptno
CONNECT BY prev = PRIOR curr AND deptno = PRIOR deptno
START WITH curr = 1;
DEPTNO EMPLOYEES
---------- --------------------------------------------------
10 CLARK,KING,MILLER
20 ADAMS,FORD,JONES,SCOTT,SMITH
30 ALLEN,BLAKE,JAMES,MARTIN,TURNER,WARD
3 rows selected.
Tim Hall 的几个很好的例子。
以下在 ORACLE 10.2.0.5.0 数据库上为我工作：
SELECT col_id, replace(wm_concat(col_text), ',', ' ') AS sentence
FROM foo
GROUP BY col_id;