如何在Oracle中自定義WMCONCAT函數(shù)

小樊
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2024-08-29 10:06:25
欄目: 云計(jì)算

在Oracle中，您可以使用用戶自定義聚合函數(shù)（User-Defined Aggregate Functions，UDAF）來(lái)實(shí)現(xiàn)類似于WM_CONCAT的功能

  1. 創(chuàng)建一個(gè)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
);
/
  1. 為聚合類型創(chuàng)建實(shí)現(xiàn)：
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;
/
  1. 創(chuàng)建用戶自定義聚合函數(shù)：
CREATE OR REPLACE FUNCTION my_wm_concat(input VARCHAR2) RETURN VARCHAR2
PARALLEL_ENABLE AGGREGATE USING my_wm_concat_type;
/

現(xiàn)在您可以在SQL查詢中像使用WM_CONCAT一樣使用MY_WM_CONCAT函數(shù)：

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

請(qǐng)注意，這個(gè)實(shí)現(xiàn)是簡(jiǎn)單的，并沒(méi)有處理所有WM_CONCAT的特性，例如排序、分隔符等。您可以根據(jù)需要對(duì)聚合類型進(jìn)行修改以實(shí)現(xiàn)更多功能。

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