The table lookup transformer allows you to look up values in a different table. Any amount of columns can be used for mapping (lookup conditioning) and for outputting (the outcome of the lookup).
The configuration screen for the table lookup transformer looks like this:
To make the mapping you need to select the target datastore, schema and table names. Once selected you will be able to select which columns to use for condition setting when looking up values.
The semantics of the Table lookup are close to the semantics of a LEFT JOIN. If no lookup value is found, nulls will be returned. However, if multiple records are found to match the conditions, only the first will be returned.
Note that the Table lookup will use a cache for looking up values, to avoid querying the target table for every incoming value.