KB31033: "CompUnit is empty. The join tree is empty. Please check if the metric has calculation level" error message appears when executing a report that contains a metric with only constant values in MicroStrategy 9.x

SYMPTOM:
When executing a report with a metric attempting to calculate a constant value the following error appears:
 

 
Sample Code/Error
Error: SQLEngine got an Exception from DFC: Engine Logic: ERROR: CompUnit is empty. The join tree is empty. Please check if the metric has calculation level.
Error in Process method of Component: SQLEngineServer
 
 
CAUSE:
Strategy cannot generate SQL for the metric object. Each metric is related to a particular table through the fact/s attribute/s used in the metric definition. When a metric contains no level as part of its definition, the action performed by the metric is to perform aggregation across the entire fact table, depending on the aggregation function used.
 

 
Having no level and no fact causes Strategy to be unable to generate valid SQL, as there is no warehouse table that can be related to the metric object. This is not an issue with Strategy as it is working as expected.
 
ACTION:
Perform one of these two actions:

• Include level information on the constant metric.
• Provide a fact as part of the aggregation function parameters.