Types of Expressions in MDX

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An MDX statement contains expressions that operate on sets, tuples, members, numbers, and strings. These expressions form the basis of the OLE DB for OLAP ability to provide a rich and powerful syntax for specifying datasets.

MDX statements operate on the following basic entities:

  • Set. A set is a collection of tuple elements. A set value expression operates on member, tuple, and set elements to yield other sets. A numeric function operates on a set element and yields a number. For example, the function SUM({USA, France}, Sales) operates on the set {USA, France} and yields the sum of Sales. A tuple value expression operates on a set element and yields tuple elements.

  • Member. This represents a member of a dimension. A member value expression can operate on a member element, which yields other member elements. For example, Boston.Parent yields the parent of the member Boston, which is Massachusetts.

  • Tuple. A tuple is a collection of members from different dimensions. For example, (Boston, [1995]) is a tuple formed by members of two dimensions: Geography and Time. A single member is a degenerated case of a tuple and can be used as an expression without the parentheses.

  • Number. A number can be an exact numeric, such as integer or decimal, or an approximate numeric, such as a float or double. You can compose numbers by the usual operators of addition, subtraction, multiplication, and division to yield other numbers. These compositions constitute numeric value expression elements.

  • Time dimension. The time series functions operate on the dimension that is specified implicitly as part of their <set>, <member>, or <level> arguments. (The time series functions described in this section are, in fact, member, set, or numeric functions.)