Limited Support for Relational Functions When Used with OLAP Data Sources
substringand concatenation functions, in a report that also contains a measure with the Aggregate Function property set to Calculated or Automatic in the model. If you do so, you may encounter unexpected results. For example, some summaries are calculated using the Minimum function instead of the aggregate function derived from the individual query items.
In the expression editor, an exclamation mark (!) that precedes a function indicates that the function is not naturally supported for that data source. IBM® Cognos® Analytics uses a local approximation for that function. Because an approximation is used, performance can be degraded and the results may not be what you expect.