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MDX Essentials: Basic Set Functions: The Union() Function - Page 4

November 10, 2003

The behavior of the Union() function is demonstrated in its elimination of the duplicate Bellingham member - a characteristic that is the default of the primary syntax with which we have been working. We note, too, that the duplicate is deleted from the "tail"; the last of the duplicate pair is the one that is "dropped."

We can prove this to ourselves by overriding the default behavior, and using the ALL flag to allow the duplicate to be retained. To do so, we will make an adjustment to the query we created in Step 4 above.

5.  Insert a comma, and then the word "ALL" into the second set specification within the Union() function, that is:

{[Store].[All Stores].[USA].[WA].[Bellingham]})  

between the right-most curly brace and the closing parenthesis, as shown:

{[Store].[All Stores].[USA].[WA].[Bellingham]},ALL)

6.  Modify the comment line to read:

-- MDX13-5:  Tutorial Query Step 5

The Query pane appears as shown in Illustration 5.


Illustration 5: The Query with Modifications Circled

7.  Execute the query by clicking the Run Query button in the toolbar.

The Results pane is populated, and the dataset shown in Illustration 6 appears. We see the "tail" instance of the duplicate Bellingham set is retained, thanks to the insertion of the ALL flag into our Union() function.


Illustration 6: Union() Function Results - Duplicates Retained via the ALL Flag

8.  Save the file as MDX13-5.

And so we see how to retain duplicates in a simple example that illustrates the influence of the ALL flag upon the Union() function. Let's turn now to the alternate syntaxes, both to examine them in general as options we might use, and to explore their implicit default behavior with regard to handling duplicates.

9.  Select File --> New from the main menu of the Sample Application.

A blank query pane appears.

10.  Type the following query into the Query pane:

-- MDX13-6:  Tutorial Query Step 6

SELECT

{[Measures].[Warehouse Sales]} ON COLUMNS,

({[Store].[All Stores].[USA].[WA].Children} +

{[Store].[All Stores].[USA].[WA].[Bellingham]})

ON ROWS

FROM Warehouse

The Union() function is called into action this time using one of two alternate syntaxes. In this approach, we use the "+" operator to effect the Union() function, with a noteworthy characteristic of this arrangement being that the UNION keyword is not used at all. Let's take a look at the results we obtain through the use of this alternate approach.

11.  Execute the query by clicking the Run Query button in the toolbar.

The Results pane is populated, and the dataset shown in Illustration 7 appears.


Illustration 8: Union() Function Results - Alternate Using "+" Operator

12.  Save the file as MDX13-6.

Although the Books Online state that "Duplicated members are always retained when an alternate syntax is used," we see clearly in the foregoing results that the duplicate has been eliminated, just as it was using the primary syntax (default scenario.) Now let's attempt the same operation with the other alternative option in a final query.

13.  Select File --> New from the main menu.

A blank query pane appears.

14.  Type the following query into the Query pane:

-- MDX13-7:  Tutorial Query Step 7

SELECT

{[Measures].[Warehouse Sales]} ON
COLUMNS,

{{[Store].[All Stores].[USA].[WA].Children},

{[Store].[All Stores].[USA].[WA].[Bellingham]}}

ON ROWS

FROM Warehouse 

The Union() function is enacted in this query using the second of two alternate syntaxes. In this approach, we simply list the sets inside the braces, separated by a comma. Again, we note that the UNION keyword is not used at all. Let's see how duplicates are handled when performing a union via this alternate option.

15.  Execute the query by clicking the Run Query button in the toolbar.

The Results pane is populated, and the dataset shown in Illustration 8 appears.


Illustration 8: Union() Function Results - Alternate Using the "List" Approach

16.  Save the file as MDX13-7.

In this case, we note that the duplicate, tail instance of Bellingham is retained, much as it was when using the ALL flag within the primary syntax example above.

In conclusion, we can see that the Union() function, both in its primary and alternate syntax forms, provides us the significant capability of performing combinations of sets. Our selection of an alternate syntax, or of the use of the optional ALL flag in the primary syntax, can also afford us flexibility in the handling of duplicates in queries we construct that use this function.

Summary ...

In this lesson, we explored the commonly used Union() function, whose purpose it is to combine two sets into one. We discussed the Union() function in general, and emphasized its provision for important capabilities within MDX, and its value within our analysis toolsets.

In addition to discussing the purpose and operation of the Union() function, we examined both primary and alternate syntaxes involved in its use, illustrating the application of each in practice exercises. Focusing on the treatment of duplicates in each of the syntactical approaches, we discussed the results we obtained in each exercise, remarking on distinguishing characteristics of each.

» See All Articles by Columnist William E. Pearson, III

Discuss this article in the MSSQL Server 2000 Analysis Services and MDX Topics Forum.

MDX Essentials Series
The LEVEL_NUMBER Member Property
The LEVEL_UNIQUE_NAME Intrinsic Member Property
Intrinsic Member Properties: The HIERARCHY_UNIQUE_NAME Property
Intrinsic Member Properties: The DIMENSION_UNIQUE_NAME Property
Further Combination of BottomCount() with Other MDX Functions
Combine BottomCount() with Other MDX Functions to Add Sophistication
Basic Set Functions: The BottomCount() Function, Part I
Intrinsic Member Properties: The MEMBER_VALUE Property
Intrinsic Member Properties: The MEMBER_UNIQUE_NAME Property
Intrinsic Member Properties: The MEMBER_NAME Property
Intrinsic Member Properties: The MEMBER_KEY Property
Intrinsic Member Properties: The MEMBER_CAPTION Property
Set Functions: The StripCalculatedMembers() Function
Set Functions: The AddCalculatedMembers() Function
MDX Numeric Functions: The Min() Function
MDX Numeric Functions: The Max() Function
Set Functions: The .AllMembers Function
MDX Essentials: Set Functions: The MeasureGroupMeasures() Function
String Functions: The .Properties Function, Part II
String Functions: The .Properties Function
Logical Functions: IsGeneration(): Conditional Logic within Filter Expressions
MDX Scripting Statements: Introducing the Simple CASE Statement
Logical Functions: IsGeneration(): Conditional Logic within Calculations
Logical Functions: IsAncestor(): Conditional Logic within Filter Expressions
MDX Clauses and Keywords: Use HAVING to Filter an Axis
Logical Functions: IsAncestor(): Conditional Logic within Calculations
Logical Functions: IsSibling(): Conditional Logic within Filter Expressions
Logical Functions: IsSibling(): Conditional Logic within Calculations
MDX Operators: The IsLeaf() Operator: Conditional Logic within Filter Expressions
MDX Operators: The IsLeaf() Operator: Conditional Logic within Calculations
MDX Numeric Functions: The .Ordinal Function
Other MDX Entities: Perspectives
MDX Operators: The IS Operator
MDX Set Functions: The Distinct() Function
MDX Set Functions: The ToggleDrillState() Function
Set Functions: The DrillUpLevel() Function
Set Functions: The DrillDownLevelTop() and DrillDownLevelBottom() Functions
MDX Set Functions: DrillDownLevel()
MDX Set Functions: The DRILLUPMEMBER() Function
MDX Essentials: Set Functions: The DRILLDOWNMEMBERTOP() and DRILLDOWNMEMBERBOTTOM() Functions
MDX Essentials : Set Functions: The DRILLDOWNMEMBER() Function
MDX Essentials: Drilling Through with MDX: The DRILLTHROUGH Statement
MDX Essentials: String Functions: The .UniqueName Function
MDX Essentials: String Functions: The .Name Function
MDX Essentials: String / Numeric Functions: The CoalesceEmpty() Function
MDX Essentials: Basic Set Functions: The TopCount() Function, Part II
MDX Essentials: Basic Set Functions: The TopCount() Function, Part I
MDX Essentials: Enhancing CROSSJOIN() with Calculated Members
MDX Essentials: Set and String Functions: The GENERATE() Function
MDX Essentials: The CROSSJOIN() Function: Breaking Bottlenecks
MDX Essentials: String / Numeric Functions: More on the IIF() Function
MDX Essentials: String / Numeric Functions: Introducing the IIF() Function
MDX Essentials: Logical Functions: The IsEmpty() Function
MDX Essentials: Basic Set Functions: The EXTRACT() Function
MDX Essentials: Numeric Functions: Introduction to the AVG() Function
MDX Essentials: Basic Member Functions: The .Item() Function
MDX Essentials: Basic Set Functions: Subset Functions: The Subset() Function
MDX Essentials: Basic Set Functions: Subset Functions: The Tail() Function
MDX Essentials: Basic Set Functions: Subset Functions: The Head() Function
MDX Essentials: Basic Set Functions: The CrossJoin() Function
MDX Essentials: Basic Numeric Functions: The Count() Function
MDX Essentials: Basic Set Functions: The Filter() Function
MDX Essentials: Basic Set Functions: The EXCEPT() Function
MDX Essentials: Basic Set Functions: The Intersect() Function
MDX Essentials: Basic Set Functions: The Union() Function
MDX Essentials: Basic Set Functions: The Order() Function
MDX Essentials - MDX Time Series Functions, Part III: The LastPeriods() and ParallelPeriod() Functions
MDX Time Series Functions, Part II: The OpeningPeriod () and ClosingPeriod() Functions
MDX Essentials - MDX Time Series Functions, Part I: PeriodsToDate() and Kindred Functions
MDX Essentials: MDX Member Functions: "Relative" Member Functions
MDX Member Functions: The Cousin () Function
MDX Essentials: Member Functions: More "Family" Functions
MDX Member Functions: The "Family" Functions
MDX Essentials: MDX Members: Introducing Members and Member
MDX Essentials : MDX Operators: The Basics
MDX Essentials: Structure of the MDX Data Model
MDX at First Glance: Introduction to SQL Server MDX Essentials








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