在Oracle中，您可以使用用戶自定義聚合函數（User-Defined Aggregate Functions，UDAF）來實現類似于WM_CONCAT的功能

1. 創建一個聚合類型：

CREATE OR REPLACE TYPE my_wm_concat_type AS OBJECT (
  concatenated_string VARCHAR2(32767),

  STATIC FUNCTION ODCIAggregateInitialize(sctx IN OUT my_wm_concat_type) RETURN NUMBER,
  MEMBER FUNCTION ODCIAggregateIterate(self IN OUT my_wm_concat_type, value IN VARCHAR2) RETURN NUMBER,
  MEMBER FUNCTION ODCIAggregateTerminate(self IN my_wm_concat_type, returnValue OUT VARCHAR2, flags IN NUMBER) RETURN NUMBER,
  MEMBER FUNCTION ODCIAggregateMerge(self IN OUT my_wm_concat_type, sctx2 IN my_wm_concat_type) RETURN NUMBER
);
/

2. 為聚合類型創建實現：

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

  MEMBER FUNCTION ODCIAggregateIterate(self IN OUT my_wm_concat_type, value IN VARCHAR2) RETURN NUMBER IS
  BEGIN
    IF self.concatenated_string IS NULL THEN
      self.concatenated_string := value;
    ELSE
      self.concatenated_string := self.concatenated_string || ',' || value;
    END IF;
    RETURN ODCIConst.Success;
  END;

  MEMBER FUNCTION ODCIAggregateTerminate(self IN my_wm_concat_type, returnValue OUT VARCHAR2, flags IN NUMBER) RETURN NUMBER IS
  BEGIN
    returnValue := self.concatenated_string;
    RETURN ODCIConst.Success;
  END;

  MEMBER FUNCTION ODCIAggregateMerge(self IN OUT my_wm_concat_type, sctx2 IN my_wm_concat_type) RETURN NUMBER IS
  BEGIN
    IF sctx2.concatenated_string IS NOT NULL THEN
      IF self.concatenated_string IS NULL THEN
        self.concatenated_string := sctx2.concatenated_string;
      ELSE
        self.concatenated_string := self.concatenated_string || ',' || sctx2.concatenated_string;
      END IF;
    END IF;
    RETURN ODCIConst.Success;
  END;
END;
/

3. 創建用戶自定義聚合函數：

CREATE OR REPLACE FUNCTION my_wm_concat(input VARCHAR2) RETURN VARCHAR2
PARALLEL_ENABLE AGGREGATE USING my_wm_concat_type;
/

現在您可以在SQL查詢中像使用WM_CONCAT一樣使用MY_WM_CONCAT函數：

SELECT deptno, MY_WM_CONCAT(ename)
FROM emp
GROUP BY deptno;

請注意，這個實現是簡單的，并沒有處理所有WM_CONCAT的特性，例如排序、分隔符等。您可以根據需要對聚合類型進行修改以實現更多功能。