We use lookup transformation to lookup data from a relational table, view, synonym or flatfile against another or the same table, view, synonym or flatfile.
This is mainly(not only)used for SCDs. So that the value in the source can be compared with the existing target.
Lookup transformation are of different types named and unnamed.
Mostly used lookup transformation types are Connected lookup (Persistent Lookup, Dynamic lookup, Cached lookup, Uncached lookup)
Lookup is a transformation to look up the values from a relational table/view or a flat file. The developer defines the lookup match criteria.
There are two types of Lookups in Powercenter-Designer
1) Connected Lookup
2) Unconnected Lookup.
Different caches can also be used with lookup like static, dynamic, persistent, and shared.