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Aggregate Product function extends SQL

, 14 Mar 2011 CPOL
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Technique to extend capability of standard SQL by adding the Aggregate Product Function


The suggested solution extends the capability of Structured Query Language (SQL) by adding the Aggregate Product function. Entire 'pure SQL' solution is encapsulated into a single query, portable to any SQL backed databases, for example, Microsoft Access or SQL Server.

1. Underlying Math Transforms

Standard SQL contains several aggregate functions (Sum, Count, Min, Max, etc.) with noticeable absence of aggregate Product. As a reminder, Product function P of multiple arguments (X1, X2,...XN) is defined as:
P(Xi)=X1*X2*...XN .................................................(1)
Database engine cannot perform the aggregate product calculation directly, but it can calculate sums. Simple mathematical transforms provide a workaround enabling to compute the product P by using the standard built-in mathematical Log(), Exp() and SQL aggregated Sum() functions; the core technique is illustrated by mathematical formulas (2) and (3):
Log(X1*X2*... XN)= Log(X1)+Log(X2)+...Log(XN) ......................(2),
N           N
P(Xi)= Exp(SUM(Log(Xi))) ............................................(3)
i=1         i=1
The last formula (3) could be translated into SQL statement in a rather straightforward manner, enabling the calculation of aggregate Product by means of standard built-in SQL functions.

2. Programming Technique: Math-to-SQL Translation

This simple yet practical example will demonstrate the SQL programming technique enabling to calculate the Product of all positive numbers {2, 4, 5, 7, 8} stored in a Microsoft Access Table1. Based on the precondition that there are no any negative values, a simple SQL query can do the job of calculating Product (SQL 1):
SELECT Exp(Sum(Log([Num]))) AS P FROM Table1
The statement could be modified with IIf() conditional operator added in order to handle zeros(SQL 2):
SELECT Exp(Sum(IIf([Num]=0,0,Log([Num]))))*IIf(Min([Num])=0,0,1) AS P
FROM Table1
The solution has been implemented/tested in Microsoft Access 2003/2007; it is also portable to any other SQL-backed Database. For detailed discussion of this SQL technique, please refer to the online article [1], published by the author and included in the reference section.


1. Aggregate Product function extends SQL[^]


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

President Infosoft International Inc
United States United States
Dr. A. Bell has 20+ years of Software and Electrical Engineering experience: Win/Web veteran published 300+ articles and authored 37 inventions, currently focused on: Windows 7/8, HTML5, CSS3, jQuery, .NET, ASP.NET, WPF, C#, SQL, 'Big Data', AI, Speech Technology and Mobile apps. He participated in App Innovation Contest (AIC 2102/2013) with several winning submissions. Sample pubs follow:
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Comments and Discussions

GeneralMy vote of 5 PinmemberScott Burkow20-Feb-13 8:31 
GeneralRe: My vote of 5 PinmemberDrABELL20-Feb-13 19:46 
GeneralRe: My vote of 5 PinmemberScott Burkow21-Feb-13 9:21 
GeneralRe: My vote of 5 PinmemberDrABELL21-Feb-13 12:39 
GeneralRe: My vote of 5 PinmemberScott Burkow22-Feb-13 6:56 
GeneralRe: My vote of 5 PinmemberDrABELL22-Feb-13 8:44 
GeneralRe: My vote of 5 PinmemberScott Burkow22-Feb-13 9:40 
GeneralReason for my vote of 5 Excellent example of using a little ... PinmemberMacMaverick23-Mar-11 2:51 
GeneralRe: Many thanks! Kind regards/wishes, Alex PinmemberDrABELL23-Mar-11 4:57 
GeneralReason for my vote of 5 Simple & unusual PinmemberA.J.Wegierski14-Mar-11 20:52 
GeneralRe: Many thanks! PinmemberDrABELL15-Mar-11 4:33 
GeneralShort URL to the article: PinmemberDrABELL4-Jan-11 10:37 

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