You can pass multiple input values into a Lookup transformation and return one column of data. Do not configure the lookup policy to use all values on multiple matches for an unconnected Lookup transformation. Designate one lookup/output port as a return port. You can choose to use the first, last, or any value that matches the lookup condition.
If you call the unconnected lookup from an update strategy or filter expression, you are generally checking for null values. In this case, the return port can be anything. If you call the lookup from an expression performing a calculation, the return value needs to be the value you want to include in the calculation.
To continue the update strategy example, you can define the ITEM_ID port as the return port. The update strategy expression checks for null values returned. If the lookup condition is true, the Integration Service returns the ITEM_ID. If the condition is false, the Integration Service returns NULL.
The following figure shows a return port in a Lookup transformation: