Combinación de varias dimensiones en ejes
Supongamos ...
Let's say that a group of FoodMart information consumers, whose data is housed within the Warehouse cube, wish to see the total Units Shipped by U.S. Warehouse-State for each quarter of 1998. Furthermore, the consumers wish to see the Units Shipped in a single column in the report, and the Quarter / Warehouse-State information in the row axis of the presentation.
The general purpose of the CrossJoin() function is to allow us to produce all combinations of two sets. and cited its common use to "collapse" two or more dimensions onto a single axis for purposes of presenting multidimensional data in a two-dimensional matrix.
the CrossJoin() function "returns the cross product of two sets." CrossJoin() is particularly handy as it allows us to prepare data for presentation in a matrix format - the need to return "all possible combinations" of the members / tuples of two or more sets is common.
he result of the use of such a cross product is the placement of two dimensions on the same axis, be it columns or rows, where CrossJoin() creates a new set made up of all possible combinations (after the manner of a "Cartesian product") of the original sets' members.
CrossJoin() handles only two dimensions at a time, so if we need to perform a cross product across more than two dimensions, we must nest the functions to realize our aims
Furthermore, the two sets upon which we are performing a cross join must exist in separate dimensions
Uses of the CrossJoin() function can be quite sophisticated, and, as we shall learn, its use should be tempered with an understanding of its potential impact upon performance.