Use the Expression transformation to calculate values in a single row. For example, you might need to adjust employee salaries, concatenate first and last names, or convert strings to numbers. You can also use the Expression transformation to test conditional statements before you pass the results to a target or other transformations. The Expression transformation is a passive transformation.
Use the Expression transformation to perform non-aggregate calculations. To perform calculations involving multiple rows, such as sums or averages, use the Aggregator transformation.
The following figure shows a simple mapping with an Expression transformation used to concatenate the first and last names of employees from the EMPLOYEES table:
You can evaluate expressions that you configure in the Expression Editor.