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TopSum (DMX)

  • Artikkeli

Applies to: SQL Server Analysis Services

Returns, in order of decreasing rank, the top-most rows of a table whose cumulative total is at least a specified value.

Syntax

  
TopSum(<table expression>, <rank expression>, <sum>)

Applies To

An expression that returns a table, such as a <table column reference>, or a function that returns a table.

Return Type

<table expression>

Remarks

The TopSum function returns the top-most rows in decreasing order of rank based on the evaluated value of the <rank expression> argument for each row, such that the sum of the <rank expression> values is at least the given total that is specified by the <sum> argument. TopSum returns the smallest number of elements possible while still meeting the specified sum value.

Examples

The following example creates a prediction query against the Association model that you build by using the Basic Data Mining Tutorial.

To understand how TopPercent works, it might be helpful to first execute a prediction query that returns only the nested table.

SELECT Predict ([Association].[v Assoc Seq Line Items], INCLUDE_STATISTICS, 10)  
FROM   
     [Association]  
NATURAL PREDICTION JOIN  
SELECT (SELECT 'Women''s Mountain Shorts' as [Model]) AS [v Assoc Seq Line Items]) AS t

Note

In this example, the value supplied as input contains a single quotation mark, and therefore must be escaped by prefacing it with another single quotation mark. If you are not sure of the syntax for inserting an escape character, you can use the Prediction Query Builder to create the query. When you select the value from the dropdown list, the required escape character is inserted for you. For more information, see Create a Singleton Query in the Data Mining Designer.

Example results:

Model $SUPPORT $PROBABILITY $ADJUSTEDPROBABILITY
Sport-100 4334 0.291283016 0.252695851
Water Bottle 2866 0.192620472 0.175205052
Patch kit 2113 0.142012232 0.132389356
Mountain Tire Tube 1992 0.133879965 0.125304948
Mountain-200 1755 0.117951475 0.111260823
Road Tire Tube 1588 0.106727603 0.101229538
Cycling Cap 1473 0.098998589 0.094256014
Fender Set - Mountain 1415 0.095100477 0.090718432
Mountain Bottle Cage 1367 0.091874454 0.087780332
Road Bottle Cage 1195 0.080314537 0.077173962

The TopSum function takes the results of this query and returns the rows with the greatest values that sum to the specified count.

SELECT   
TopSum  
    (  
    Predict([Association].[v Assoc Seq Line Items],INCLUDE_STATISTICS,10),  
    $PROBABILITY,  
    .5)  
FROM   
     [Association]  
NATURAL PREDICTION JOIN  
(SELECT (SELECT 'Women''s Mountain Shorts' as [Model]) AS [v Assoc Seq Line Items]) AS t

The first argument to the TopSum function is the name of a table column. In this example, the nested table is returned by calling the Predict function and using the INCLUDE_STATISTICS argument.

The second argument to the TopSum function is the column in the nested table that you use to order the results. In this example, the INCLUDE_STATISTICS option returns the columns $SUPPORT, $PROBABILITY, and $ADJUSTED PROBABILITY. This example uses $PROBABILITY to return rows that sum to at least 50% probability.

The third argument to the TopSum function specifies the target sum, as a double. To get the rows for the top products that sum to 50 percent probability, you type .5.

Example results:

Model $SUPPORT $PROBABILITY $ADJUSTEDPROBABILITY
Sport-100 4334 0.29... 0.25...
Water Bottle 2866 0.19... 0.17...
Patch kit 2113 0.14... 0.13...

Note This example is provided only to illustrate the usage of TopSum. Depending on the size of your data set, this query might take a long time to run.

See Also

Functions (DMX)
General Prediction Functions (DMX)
TopPercent (DMX)