WMSYS.WM_CONCAT函数是oracle的内部函数，不建议客户直接使用。在12c版本以后，更是把这个函数移除了。

今天就碰上一位朋友，应用里面必须要用到WMSYS.WM_CONCAT这个函数，导致无法升级到19c。

针对这种问题，oracle也给了一些解决方案。

• 使用listagg函数代替WM_CONCAT函数
• 使用自定义函数

自定义函数如下：

WM_CONCAT Built-in Function (Not Supported)

If you are not running 11g Release 2 or above, but are running a version of the database where the WM_CONCAT function is present, then it is a zero effort solution as it performs the aggregation for you. It is actually an example of a user defined aggregate function described below, but Oracle have done all the work for you.

COLUMN employees FORMAT A50

SELECT deptno, wm_concat(ename) AS employees
FROM   emp
GROUP BY deptno;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,FORD,ADAMS,SCOTT,JONES
        30 ALLEN,BLAKE,MARTIN,TURNER,JAMES,WARD

3 rows selected.

User-Defined Aggregate Function

The WM_CONCAT function described above is an example of a user-defined aggregate function that Oracle have already created for you. If you don't want to use WM_CONCAT, you can create your own user-defined aggregate function as described at asktom.oracle.com. Thanks to Kim Berg Hansen for some corrections in comments.

CREATE OR REPLACE TYPE t_string_agg AS OBJECT
(
  g_string  VARCHAR2(32767),

  STATIC FUNCTION ODCIAggregateInitialize(sctx  IN OUT  t_string_agg)
    RETURN NUMBER,

  MEMBER FUNCTION ODCIAggregateIterate(self   IN OUT  t_string_agg,
                                       value  IN      VARCHAR2 )
     RETURN NUMBER,

  MEMBER FUNCTION ODCIAggregateTerminate(self         IN   t_string_agg,
                                         returnValue  OUT  VARCHAR2,
                                         flags        IN   NUMBER)
    RETURN NUMBER,

  MEMBER FUNCTION ODCIAggregateMerge(self  IN OUT  t_string_agg,
                                     ctx2  IN      t_string_agg)
    RETURN NUMBER
);
/
SHOW ERRORS


CREATE OR REPLACE TYPE BODY t_string_agg IS
  STATIC FUNCTION ODCIAggregateInitialize(sctx  IN OUT  t_string_agg)
    RETURN NUMBER IS
  BEGIN
    sctx := t_string_agg(NULL);
    RETURN ODCIConst.Success;
  END;

  MEMBER FUNCTION ODCIAggregateIterate(self   IN OUT  t_string_agg,
                                       value  IN      VARCHAR2 )
    RETURN NUMBER IS
  BEGIN
    SELF.g_string := self.g_string || ',' || value;
    RETURN ODCIConst.Success;
  END;

  MEMBER FUNCTION ODCIAggregateTerminate(self         IN   t_string_agg,
                                         returnValue  OUT  VARCHAR2,
                                         flags        IN   NUMBER)
    RETURN NUMBER IS
  BEGIN
    returnValue := SUBSTR(SELF.g_string, 2);
    RETURN ODCIConst.Success;
  END;

  MEMBER FUNCTION ODCIAggregateMerge(self  IN OUT  t_string_agg,
                                     ctx2  IN      t_string_agg)
    RETURN NUMBER IS
  BEGIN
    SELF.g_string := SELF.g_string || ctx2.g_string;
    RETURN ODCIConst.Success;
  END;
END;
/
SHOW ERRORS


CREATE OR REPLACE FUNCTION string_agg (p_input VARCHAR2)
RETURN VARCHAR2
PARALLEL_ENABLE AGGREGATE USING t_string_agg;
/
SHOW ERRORS

The aggregate function is implemented using a type and type body, and is used within a query.

COLUMN employees FORMAT A50

SELECT /*+ PARALLEL(2) */ deptno, string_agg(ename) AS employees
FROM   emp
GROUP BY deptno;

    DEPTNO EMPLOYEES
---------- --------------------------------------------------
        10 CLARK,KING,MILLER
        20 SMITH,FORD,ADAMS,SCOTT,JONES
        30 ALLEN,BLAKE,MARTIN,TURNER,JAMES,WARD

3 rows selected.

【参考资料】

Unable To Run Custom Report Under Company Level Reporting Tab. Data View Using SQL function "wm_concat" Not Supported. (Doc ID 2149649.1)

WMSYS.WM_CONCAT Should Not Be Used For Customer Applications, It Is An Internal Function (Doc ID 1336219.1)

WM_CONCAT Vs LISTAGG - ORA-00904: "WM_CONCAT": invalid identifier (Doc ID 2622063.1)

WMSYS Packages/Functions missing on 12c (Doc ID 2368194.1)

https://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:2196162600402

https://oracle-base.com/articles/misc/string-aggregation-techniques#wm_concat

http://docs.oracle.com/cd/E11882_01/server.112/e41084/functions089.htm#SQLRF30030