oracle提供了聚合函數的API可以讓我們方便的自己定義聚合函數。

詳細看oracle官方文檔：

http://docs.oracle.com/cd/B14117_01/appdev.101/b10800/dciaggref.htm

http://docs.oracle.com/cd/B14117_01/appdev.101/b10800/dciaggfns.htm#g1008306

wmsys.wm_concat(合并行函數)是一個很好的例子：

FUNCTION wm_concat(P1 VARCHAR2) RETURN CLOB AGGREGATE USING WMSYS.WM_CONCAT_IMPL ;

TYPE wm_concat_impl AUTHID CURRENT_USER AS OBJECT

(

CURR_STR ? ?VARCHAR2(32767),

CURR_STR_C ?CLOB,

STATIC FUNCTION ODCIAGGREGATEINITIALIZE(SCTX IN OUT WM_CONCAT_IMPL) RETURN NUMBER,

MEMBER FUNCTION ODCIAGGREGATEITERATE(SELF IN OUT WM_CONCAT_IMPL, P1 VARCHAR2) RETURN NUMBER,

MEMBER FUNCTION ODCIAGGREGATETERMINATE(SELF WM_CONCAT_IMPL, RETURNVALUE OUT CLOB, FLAGS NUMBER) RETURN NUMBER,

MEMBER FUNCTION ODCIAGGREGATEMERGE(SELF IN OUT WM_CONCAT_IMPL, SCTX2 WM_CONCAT_IMPL) RETURN NUMBER

);

TYPE BODY wm_concat_impl IS

STATIC FUNCTION ODCIAGGREGATEINITIALIZE(SCTX IN OUT WM_CONCAT_IMPL) RETURN NUMBER IS

BEGIN

SCTX := WM_CONCAT_IMPL(NULL,NULL) ;

RETURN ODCICONST.SUCCESS;

END;

MEMBER FUNCTION ODCIAGGREGATEITERATE(SELF IN OUT WM_CONCAT_IMPL, P1 VARCHAR2) RETURN NUMBER IS

BEGIN

IF (CURR_STR_C IS NULL AND (CURR_STR IS NULL OR LENGTH(CURR_STR)<29950)) THEN

IF(CURR_STR IS NOT NULL) THEN

CURR_STR := CURR_STR || ',' || P1;

ELSE

CURR_STR := P1;

END IF;

ELSE

IF (CURR_STR_C IS NULL) THEN

CURR_STR_C := CURR_STR ;

CURR_STR := NULL ;

END IF ;

CURR_STR_C := CURR_STR_C || ',' || P1;

END IF ;

RETURN ODCICONST.SUCCESS;

END;

MEMBER FUNCTION ODCIAGGREGATETERMINATE(SELF WM_CONCAT_IMPL, RETURNVALUE OUT CLOB, FLAGS NUMBER) RETURN NUMBER IS

BEGIN

IF (CURR_STR IS NOT NULL) THEN

RETURNVALUE := CURR_STR ;

ELSE

RETURNVALUE := CURR_STR_C ;

END IF ;

RETURN ODCICONST.SUCCESS;

END;

MEMBER FUNCTION ODCIAGGREGATEMERGE(SELF IN OUT WM_CONCAT_IMPL, SCTX2 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;

來自 “ ITPUB博客 ” ，鏈接：http://blog.itpub.net/195110/viewspace-1682558/，如需轉載，請注明出處，否則將追究法律責任。

總結

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