Oracle聚合求和和聚合求积(顺便解决BOM展开的问题)

本文参考网址：http://www.itpub.net/thread-1020772-1-1.html

我们在日常的工作中，经常遇到了针对某一列的值，进行求和，求平均值，在一些特殊的业务场景下，我们需要对某一列进行求积操作，那我们该如何实现呢，下面先介绍，我

们对字符串的求和操作。

针对字符串的求和操作：

1、有分隔符的字符串：

 SELECT STR, SUM(STR) OVER(ORDER BY LV ASC) AS RS
   FROM (SELECT REGEXP_SUBSTR('1,2,3,4,5', '[^,]+', 1, LEVEL) AS STR,
                LEVEL AS LV
           FROM DUAL
         CONNECT BY LEVEL <=
                    LENGTH(REGEXP_REPLACE('1,2,3,4,5', '[^,]', '')) + 1) COLS

结果：
 

2、没有分割符符号的：

       SELECT STR, SUM(STR) OVER(ORDER BY LV ASC) AS RS
         FROM (SELECT SUBSTR('', LEVEL, 1) STR, LEVEL AS LV
                 FROM DUAL
               CONNECT BY LEVEL <= LENGTH(12345)) COLS

结果：

下面介绍连续求积的方法

SUM()是个求和的聚合函数，如何求积呢？我们可以想办法把乘法变成加法：

A*B*C = 10^(LOG(A)+LOG(B)+LOG(C))

1、直接使用对数和反对数来进行求积，即：LOG和POWER函数

 SELECT STR, POWER(10, SUM(LOG(10, STR)) OVER(ORDER BY STR))
   FROM (SELECT REGEXP_SUBSTR('1,2,3,4,5', '[^,]+', 1, LEVEL) AS STR,
                LEVEL AS LV
           FROM DUAL
         CONNECT BY LEVEL <=
                    LENGTH(REGEXP_REPLACE('1,2,3,4,5', '[^,]', '')) + 1) COLS

结果：

2、使用PL/SQL的自定义函数来实现该功能

 CREATE OR REPLACE FUNCTION GET_EXPRESSION_RSLT(I_EXPRESSION VARCHAR2) RETURN VARCHAR2 IS
  /************************************************************
   * 函数名称：GET_EXPRESSION_RSLT
   * 功能描述：获取指定的表达式的结果
   * 参数：I_EXPRESSION :表达式  例如：1*2*3
   * 编 写 人：XXX
   * 编写时间：XXXX-XX-XX
   * 修改记录：
   *************************************************************/
     RETURNSTR VARCHAR2(500) := '';
     EXECSQL   VARCHAR2(4000) := '';
   BEGIN
     EXECSQL := ' SELECT ' || I_EXPRESSION || '  FROM  DUAL';
     EXECUTE IMMEDIATE (EXECSQL)
       INTO RETURNSTR;
     RETURN RETURNSTR;
   END;

SQL:

 SELECT STR,
        GET_EXPRESSION_RSLT(REPLACE(WM_CONCAT(STR) OVER(ORDER BY STR),
                                    ',',
                                    '*')) RS
   FROM (SELECT REGEXP_SUBSTR('1,2,3,4,5', '[^,]+', 1, LEVEL) AS STR,
                LEVEL AS LV
           FROM DUAL
         CONNECT BY LEVEL <=
                    LENGTH(REGEXP_REPLACE('1,2,3,4,5', '[^,]', '')) + 1) COLS

结果：

但是，使用这种方法：newid这个大拿给出了不使用该种方法的建议：

SELECT A*B*C... FROM DUAL;

都是常量且个数不定，每次都需要硬解析，所以不推荐。

下面是tom对使用wm_concat函数的看法：

http://asktom.oracle.com/pls/ask ... #548923200346634568

Hi Tom,

I saw wm_concat on a couple of forums (otn and orafaq), apparently a new, undocumented function as
shown below.  Since it is undocumented, is it safe to use?

Regards,
Barbara

Followup   November 20, 2007 - 2pm US/Eastern:

my suggestion is going to be consistent....

Never use undocumented stuff, it is subject to change, removal, broken-ness without recourse.

either

a) use stragg
b) write your own
c) use the connect by trick.

3、使用自定义的聚合函数

安德森

 CREATE OR REPLACE TYPE PROD_AGG_TYPE AS OBJECT
 (
   TOTAL NUMBER,

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

   MEMBER FUNCTION ODCIAGGREGATEITERATE(SELF  IN OUT PROD_AGG_TYPE,
                                        VALUE IN NUMBER) RETURN NUMBER,

   MEMBER FUNCTION ODCIAGGREGATETERMINATE(SELF        IN PROD_AGG_TYPE,
                                          RETURNVALUE OUT NUMBER,
                                          FLAGS       IN NUMBER)
     RETURN NUMBER,

   MEMBER FUNCTION ODCIAGGREGATEMERGE(SELF IN OUT PROD_AGG_TYPE,
                                      CTX2 IN PROD_AGG_TYPE) RETURN NUMBER
 )
 /
 CREATE OR REPLACE TYPE BODY PROD_AGG_TYPE IS

   STATIC FUNCTION ODCIAGGREGATEINITIALIZE(SCTX IN OUT PROD_AGG_TYPE)
     RETURN NUMBER IS
   BEGIN
     SCTX       := PROD_AGG_TYPE(NULL);
     SCTX.TOTAL := 1;
     RETURN ODCICONST.SUCCESS;
   END;

   MEMBER FUNCTION ODCIAGGREGATEITERATE(SELF  IN OUT PROD_AGG_TYPE,
                                        VALUE IN NUMBER) RETURN NUMBER IS
   BEGIN
     SELF.TOTAL := SELF.TOTAL * VALUE;
     RETURN ODCICONST.SUCCESS;
   END;

   MEMBER FUNCTION ODCIAGGREGATETERMINATE(SELF        IN PROD_AGG_TYPE,
                                          RETURNVALUE OUT NUMBER,
                                          FLAGS       IN NUMBER) RETURN NUMBER IS
   BEGIN
     RETURNVALUE := SELF.TOTAL;
     RETURN ODCICONST.SUCCESS;
   END;

   MEMBER FUNCTION ODCIAGGREGATEMERGE(SELF IN OUT PROD_AGG_TYPE,
                                      CTX2 IN PROD_AGG_TYPE) RETURN NUMBER IS
   BEGIN
     SELF.TOTAL := SELF.TOTAL * CTX2.TOTAL;
     RETURN ODCICONST.SUCCESS;
   END;

 END;
 /

函数：

CREATE OR REPLACE FUNCTION prod_agg(input NUMBER )
RETURN NUMBER
PARALLEL_ENABLE AGGREGATE USING prod_agg_type;

SQL:

  SELECT STR, prod_agg(STR) OVER(ORDER BY LV ASC) AS RS
         FROM (SELECT SUBSTR('', LEVEL, 1) STR, LEVEL AS LV
                 FROM DUAL
               CONNECT BY LEVEL <= LENGTH(12345)) COLS

结果：