Semantics of Empty Cell Value

In order to precisely define the semantics of empty cells in these situations, MDX defines the concept of an empty cell value. This is a special value that  is present in the empty cell. The following rules determine the semantics of the empty cell value:

1. The function ISEMPTY(value_expression) returns TRUE if and only if value_expression is the empty cell value. Otherwise it returns FALSE.
   
   
2. When the empty cell value is an operand for any of the numeric operators (+, -, *, /), it behaves like the number zero.
   
   
3. When the empty cell value is an operand for the string concatenation operator (||), it behaves like the empty string.
   
   
4. When the empty cell value is an operand for any of the comparison operators (=. <>, >=, <=, >, <), it behaves like the number zero or the empty string, depending on whether the data type of the other operand is numeric or string, respectively.
   
   
5. When collating numeric values, the empty cell value collates in the same place as zero. Between the empty cell value and zero,  empty collates before zero.
   
   
6. When collating string values, the empty cell value collates in the same place as the empty string. Between the empty cell value and the empty string, empty collates before an empty string.