Lookup transformations are those transformations which have admission right to RDBMS based data set. The server makes the access faster by using the lookup tables to look at explicit table data or the database. Concluding data is achieved by matching the look up condition for all look up ports delivered during transformations.
It is a diverse input group transformation which can be used to combine data from different sources. It works like UNION All statement in SQL that is used to combine result set of two SELECT statements.