在 Oracle XE 10g 中使用 WMSYS.WM_CONCAT

Question

当我尝试将 WMSYS.WM_CONCAT 与 Oracle XE 10g 一起使用时，我收到一个编译错误：ORA-00904: "WMSYS"."WM_CONCAT": invalid identifier。任何人都可以验证这确实是由于 XE 缺少此（未记录的）功能吗？如果是这样，是否有在 XE 中启用它？

Answer 1

建议不要使用 WM_CONCAT，因为它是一个未记录的功能，并且已从 12c 版本中删除。见Why not use WM_CONCAT function in Oracle?

如果您使用的是 11gR2 及更高版本，请使用 LISTAGG。

对于不支持 LISTAGG 的 11g 之前的版本，您可以使用 ROW_NUMBER() 和 SYS_CONNECT_BY_PATH 函数。

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.

Answer 2

来源：link。

只需自己创建这个函数：

CREATE OR REPLACE TYPE wm_concat_impl
   AUTHID CURRENT_USER
AS OBJECT (
   curr_str   VARCHAR2 (32767),
   STATIC FUNCTION odciaggregateinitialize (sctx IN OUT wm_concat_impl)
      RETURN NUMBER,
   MEMBER FUNCTION odciaggregateiterate (
      SELF   IN OUT   wm_concat_impl,
      p1     IN       VARCHAR2
   )
      RETURN NUMBER,
   MEMBER FUNCTION odciaggregateterminate (
      SELF          IN       wm_concat_impl,
      returnvalue   OUT      VARCHAR2,
      flags         IN       NUMBER
   )
      RETURN NUMBER,
   MEMBER FUNCTION odciaggregatemerge (
      SELF    IN OUT   wm_concat_impl,
      sctx2   IN       wm_concat_impl
   )
      RETURN NUMBER
);
/

CREATE OR REPLACE TYPE BODY wm_concat_impl
IS
   STATIC FUNCTION odciaggregateinitialize (sctx IN OUT wm_concat_impl)
      RETURN NUMBER
   IS
   BEGIN
      sctx := wm_concat_impl (NULL);
      RETURN odciconst.success;
   END;
   MEMBER FUNCTION odciaggregateiterate (
      SELF   IN OUT   wm_concat_impl,
      p1     IN       VARCHAR2
   )
      RETURN NUMBER
   IS
   BEGIN
      IF (curr_str IS NOT NULL)
      THEN
         curr_str := curr_str || ',' || p1;
      ELSE
         curr_str := p1;
      END IF;

      RETURN odciconst.success;
   END;
   MEMBER FUNCTION odciaggregateterminate (
      SELF          IN       wm_concat_impl,
      returnvalue   OUT      VARCHAR2,
      flags         IN       NUMBER
   )
      RETURN NUMBER
   IS
   BEGIN
      returnvalue := curr_str;
      RETURN odciconst.success;
   END;
   MEMBER FUNCTION odciaggregatemerge (
      SELF    IN OUT   wm_concat_impl,
      sctx2   IN       wm_concat_impl
   )
      RETURN NUMBER
   IS
   BEGIN
      IF (sctx2.curr_str IS NOT NULL)
      THEN
         SELF.curr_str := SELF.curr_str || ',' || sctx2.curr_str;
      END IF;

      RETURN odciconst.success;
   END;
END;
/

CREATE OR REPLACE FUNCTION wm_concat (p1 VARCHAR2)
   RETURN VARCHAR2
   AGGREGATE USING wm_concat_impl;
/

Answer 3

我找到了几个参考站点，但没有启用它。我最终编写了自己的函数来处理连接。

CREATE or replace FUNCTION CONCAT_LIST( cur SYS_REFCURSOR, sep Varchar2 ) RETURN  VARCHAR2 IS
ret VARCHAR2(32000);
tmp VARCHAR2(4000);
BEGIN
loop
  fetch cur into tmp;
  exit when cur%NOTFOUND;
    if ret is null then
       ret := tmp;
    else
      ret := ret || sep || tmp;
    end if;

end loop;
RETURN ret; END;/

那么它可以称为

SELECT distinct CONCAT_LIST(CURSOR(SELECT id FROM test_table1), ',') test_table1 FROM dual