You can evaluate expressions that you configure in the Expression Editor of an Expression transformation. When you test an expression, you can enter sample data and then evaluate the expression.
If you edit an expression condition, you must select Refresh in the test panel before you can evaluate test data. If you do not enter a valid expression, the test panel fails to populate ports. When you specify system-defined parameters, the value that you enter is not a run-time value.
The following image displays how to evaluate a sample expression within an Expression Editor of an Expression transformation:
You cannot evaluate expressions of the Date/Time or Binary data types.
Example
You need to calculate promotional offers based on the total number of orders received for each customer before loading all the results to the target. You develop a mapping to calculate offers by defining an expression within the Expression transformation. You evaluate the expression to verify the result before the operator runs the mapping.