oracle重新wm_concat函数，字段不可为空（主要解决10g以上版本没有wm_concat函数的问题）

按照如下横线分开执行，即可：

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CREATE OR REPLACE TYPE wm_concat_LOB AS OBJECT ( 
    V_LOB CLOB, 
    STATIC FUNCTION ODCIAGGREGATEINITIALIZE(SCTX IN OUT NOCOPY wm_concat_LOB) RETURN NUMBER, 
    MEMBER FUNCTION ODCIAGGREGATEITERATE(SELF IN OUT NOCOPY wm_concat_LOB, VALUE IN VARCHAR2) RETURN NUMBER, 
    MEMBER FUNCTION ODCIAGGREGATETERMINATE(SELF IN wm_concat_LOB, RETURNVALUE OUT NOCOPY CLOB, FLAGS IN NUMBER) RETURN NUMBER, 
    MEMBER FUNCTION ODCIAGGREGATEMERGE(SELF IN OUT NOCOPY wm_concat_LOB, CTX2 IN wm_concat_LOB) RETURN NUMBER 
   )
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CREATE OR REPLACE TYPE BODY wm_concat_LOB IS 
    STATIC FUNCTION ODCIAGGREGATEINITIALIZE(SCTX IN OUT NOCOPY wm_concat_LOB) RETURN NUMBER IS 
    BEGIN 
    SCTX := wm_concat_LOB(NULL); 
    DBMS_LOB.CREATETEMPORARY(SCTX.V_LOB, TRUE, DBMS_LOB.SESSION);
   DBMS_LOB.OPEN(SCTX.V_LOB, DBMS_LOB.LOB_READWRITE);
    RETURN ODCICONST.SUCCESS; 
    END; 
    
  MEMBER FUNCTION ODCIAGGREGATEITERATE(SELF IN OUT NOCOPY wm_concat_LOB, VALUE IN VARCHAR2) RETURN NUMBER IS 
  BEGIN 
  DBMS_LOB.WRITEAPPEND(SELF.V_LOB, LENGTH(VALUE) + 1, VALUE || ','); 
 RETURN ODCICONST.SUCCESS; 
  END; 
   
  MEMBER FUNCTION ODCIAGGREGATETERMINATE(SELF IN wm_concat_LOB, RETURNVALUE OUT NOCOPY CLOB, FLAGS IN NUMBER) RETURN NUMBER IS 
  BEGIN 
  DBMS_LOB.CREATETEMPORARY(RETURNVALUE, TRUE, DBMS_LOB.CALL);
  DBMS_LOB.COPY(RETURNVALUE, SELF.V_LOB, DBMS_LOB.GETLENGTH(SELF.V_LOB) - 1);
  RETURN ODCICONST.SUCCESS;
  END; 
  
  MEMBER FUNCTION ODCIAGGREGATEMERGE(SELF IN OUT NOCOPY wm_concat_LOB, CTX2 IN wm_concat_LOB) RETURN NUMBER IS 
  BEGIN 
  NULL;
  RETURN ODCICONST.SUCCESS;
 END;
  END;
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  CREATE OR REPLACE FUNCTION wm_concat_CLOB(P_STR VARCHAR2) RETURN CLOB 
   AGGREGATE USING wm_concat_LOB; 
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  select * from sys_user
  -- SET AUTOT TRACE STAT
 SELECT  wm_concat(distinct username),wm_concat_CLOB(distinct username) FROM sys_user --WHERE ROWNUM < 10000;