A common use for unconnected Lookup transformations is to update slowly changing dimension tables. For more information about slowly changing dimension tables, visit the Informatica Knowledge Base at
The syntax for the lookup expression is
:LKP lookup_transformation_name(argument, argument, ...)
The order in which you list each argument must match the order of the lookup conditions in the Lookup transformation. The Lookup transformation returns the result of the query through the Lookup transformation return port. The transformation that calls the lookup receives the lookup result value in the port that contains the :LKP expression. If the lookup query fails to return a value, the port receives a null value.
When you perform an unconnected lookup, you can perform the same lookup multiple times in a mapping. You can test the results of the lookup in another expression and filter rows based on the results.
When you run a mapping that contains an unconnected Lookup transformation, the Integration Service performs the following steps:
An unconnected Lookup transformation receives input values from the result of a :LKP expression in another transformation, such as an Aggregator transformation, Expression transformation, or Update Strategy transformation.
The Integration Service queries the lookup source or cache based on the lookup ports and condition in the Lookup transformation.
The Integration Service returns a value through the return port of the Lookup transformation.
The Integration Service passes the return value to the port that contains the :LKP expression.