When working with multidimensional expressions (MDX) in a data warehouse environment, it is common to need to exclude certain members from a query. This can be done using a variety of techniques, but one particularly useful approach is to obtain all descendants at a higher level. In this article, we will explore how to effectively use this method to exclude a specific member from an MDX call.
Before we dive into the details, let's first clarify what we mean by "descendants at a higher level." In a multidimensional data model, members are organized in a hierarchy, with each member having a parent and potentially multiple children. Descendants at a higher level refer to all the members that are above a given member in the hierarchy, regardless of how many levels there are in between. This concept is crucial to understand when dealing with MDX queries.
So, why would we want to exclude a member from an MDX call? There are a few possible scenarios where this might be necessary. For example, imagine we have a sales data cube that includes a hierarchy for product categories, with the top level being "All Products." Now, let's say we want to run a query to obtain the sales for all products except for a specific category, such as "Electronics." This is where excluding a member using descendants at a higher level comes into play.
To achieve this, we can use the EXCEPT function in MDX, which allows us to exclude a set of members from another set. In our case, the set we want to exclude will be all the descendants at a higher level of the "Electronics" category. This ensures that all the products falling under the "Electronics" category will be excluded from our query results.
The syntax for using the EXCEPT function in MDX is as follows:
SELECT [Measures].[Sales] ON COLUMNS,
EXCEPT(
[Product].[Category].MEMBERS,
[Product].[Category].[Electronics].DESCENDANTS
) ON ROWS
FROM [Sales Cube]
Let's break down this syntax. First, we specify the "Sales" measure on the columns axis, as we want to see the sales values for each product category. Then, we use the EXCEPT function, which takes two arguments - the set to be excluded and the set to be excluded from. In our case, the first argument is the entire set of product categories, and the second argument is all the descendants at a higher level of the "Electronics" category.
By using the DESCENDANTS function, we ensure that any products falling under the "Electronics" category, regardless of how many levels down in the hierarchy they are, will be excluded from our results. This approach is highly efficient and flexible, as it allows us to exclude any given member and all its descendants at a higher level without having to specify each one individually.
In conclusion, using descendants at a higher level is a powerful technique for excluding members from an MDX call. It allows us to easily exclude a specific member and all its descendants without having to specify each one individually. This approach is particularly useful in scenarios where we need to exclude a large number of members or when the hierarchy is complex. So next time you need to exclude a member from an MDX query, remember the EXCEPT function and descendants at a higher level.
