An unconnected Lookup transformation is a Lookup transformation that is not connected to a source or target. Call the lookup from another transformation with a :LKP expression.
You can perform the following tasks when you call a lookup from an expression:
Test the results of a lookup in an expression.
Filter rows based on the lookup results.
Mark rows for update based on the result of a lookup and update slowly changing dimension tables.
Call the same lookup multiple times in one mapping.
To configure an unconnected Lookup transformation, add input ports, configure the lookup condition, designate a return value, and configure a lookup expression in a different transformation.