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MAPPINGS PAGE - TRANSFORMATION MAPPINGS - LOOKUP TRANSFORMATION

Transformation

Lookup(Lkp_)

Explanation

Lookup transformation is a passive.

Lookup transformation in a mapping to look up data in a flat file or a relational table

Lookup perform many tasks ::

Get a related value
Perform a calculation
Update slowly changing dimension tables.

Lookup Types ::

Connected or unconnected
Relational or flat file lookup.
Cached or uncached

Difference between Connected and Unconnected Lookup ::

Connected	Unconnected
Receives input values directly from the pipeline	Receives input values from the result of a :LKP expression in another transformation.
Use a dynamic or static cache	Use a static cache
Give user-defined default values	Not accepts user-defined default value
Return multiple column	Returns only one column
Pass multiple output values	Passes one output value
Cache includes all lookup columns used in the mapping	Cache includes all lookup/output ports in the lookup condition and the lookup/return port
No match for the lookup condition::returns the default value for all output ports	No match for the lookup condition:: PCS returns NULL
Match for the lookup condition::returns the result of the lookup condition for all lookup/output ports	Match for the lookup condition:: returns the result of the lookup condition into the return port

Lookup Cache ::

Persistent	we can save the lookup cache files and reuse them the next time the PCS processes a Lookup transformation configured to use the cache
Recache	If the persistent cache is not synchronized with the lookup table, you can configure the Lookup transformation to rebuild the lookup cache.
Static	It caches the lookup file or table and looks up values in the cache for each row that comes into the transformation. When the lookup condition is true, the PowerCenter Server returns a value from the lookup cache. PCS does not update the cache while it processes the Lookup transformation
Dynamic	If you want to cache the target table and insert new rows or update existing rows in the cache and the target, you can create a Lookup transformation to use a dynamic cache. The PowerCenter Server dynamically inserts or updates data in the lookup cache and passes data to the target table. You cannot use a dynamic cache with a flat file lookup.
Shared	You can share the lookup cache between multiple transformations. You can share an unnamed cache between transformations in the same mapping. You can share a named cache between transformations in the same or different mappings.

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