Lookup Transformation in Informatica

Lookup is used for data verifications in informatica. Lookup is active or passive transformation and can be used as connected and unconnected modes. Look up transformation can return single or multiple rows.
We can use the lookup to perform the following.
•Get Related value
•Get multiple values.
•Perform calculation
•Update slowly changing dimensions.

Lookup Transformation can be configure in the following types of lookup
Flat File or Relational Lookup
We can perform the lookup on the flat file or relational database. When you create a lookup using flat file as lookup source, the designer invokes flat file wizard. If you used relational table as lookup source, then we can connect to the lookup source using ODBC and import the table definition.
Cached or Uncached Lookup
Improve the performence of the lookup by caching lookup source.
In the cache lookup two types of caches are there
Static Cache: By default lookup cache is static. If there is any change in the lookup table during session execution ,static lookup will not be refreshed with the changes. The changes will be reflected from the next session execution.
Dynamic Cache : If there is any change in the lookup table during session execution , the changes will be refreshed immediately in the cache.
Connected or Unconnected Lookup
The differences between connected and unconnected lookup is

           Connected Lookup
          Unconnected Lookup
It will participate in data flow
It will not participate in data flow
Accepts input directly from a source or any other Transformation.
It will accept from expression
It can be used once in a mapping.
It can be used multiple times.
It will return multiple ports.
Returns only single port.
It supports dynamic cache.
It does not support dynamic cache.
Supports user defined default values.
It does not support user defined values.
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