MDX - Analysis Services ground rules for interpreting null values

·         Null values in measures—For each fact table measure that is loaded into the partition, you can decide how Analysis Services interprets null values. Consider the following example. Your sales fact table contains a record that has a sales amount of 1000 and a discount amount of null. When discount is loaded into the cube, by default it is interpreted as a zero, which means that it is not considered empty. How Analysis Services interprets null values is controlled by a property called NullProcessing. The NullProcessing property is set on a measure-by-measure basis. By default, it is set to Automatic which means that Analysis Services converts the null values to zero. If you want to preserve the null value from the source system, such as in the example of the discount measure, configure the NullProcessingProperty of that measure to Preserve instead of Automatic.
·         Null values in calculations—In calculations, it is important to understand how Nulls are evaluated. For example, 1 minus Null equals 1, not Null. In this example, the Null is treated like a zero for calculation purposes. which may or may not be what you want to use. To explicitly test whether a tuple is null, use the ISEmpty function within an IIF statement to conditionally handle empty tuples.
Empty members—When writing calculations that reference dimension members, you may need to handle scenarios where specific members do not exist, such as the parent of the All. In this scenario, the ISEmpty function is not appropriate as it tests for empty cells. Rather in this scenario you want to use the IS operator to test whether the member IS NULL.

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