MDX - SQL Server Analysis Services 2012 Cube Development - page 206

4. An alternate syntax for writing CROSSJOIN is a single multiplication ( *) char-
acter between each combination of sets. For example, you could rewrite the
last query as follows:
SELECT [Measures].[Reseller Sales Amount]
ON 0,
[Promotion].[Promotions].[Category].members
*
[Date].[Calendar].[Calendar Year].members
ON 1
FROM [Adventure Works]
Note
Though it is often considered to be the culmination of MDX's power,
CROSSJOIN of large sets is a rather expensive operation. You can expect
query performance to progressively worsen as you add multiple nested
CROSSJOIN functions. Although the result set could be very useful for re-
porting purposes, the performance of such queries rarely lives up to the
definition of Online Analytical Processing ( OLAP ) that expects queries
to be completed within a few seconds.