Use a Lookup
transformation in your mapping to look up data in a relational table, view, or
synonym. Import a lookup definition from any relational database to which both
the Informatica Client and Server can connect. You can use multiple Lookup
transformations in a mapping.
The Informatica
Server queries the lookup table based on the lookup ports in the
transformation. It compares Lookup transformation port values to lookup table
column values based on the lookup condition. Use the result of the lookup to
pass to other transformations and the target.
You can use the
Lookup transformation to perform many tasks, including:
a) Get a related value:
For
example, if your source table includes employee ID, but you want to include the
employee name in your target table to make your summary data easier to read.
b) Perform a calculation:
Many
normalized tables include values used in a calculation, such as gross sales per
invoice or sales tax, but not the calculated value (such as net sales).
c) Update slowly changing dimension tables:
You
can use a Lookup transformation to determine whether records already exist in
the target.
You
can configure the Lookup transformation to perform different types of lookups.
You can configure the transformation to be connected or unconnected, cached or
uncached:
a) Connected or unconnected:
Connected
and unconnected transformations receive input and send output in different
ways.
b) Cached or uncached:
Sometimes
you can improve session performance by caching the lookup table. If you cache
the lookup table, you can choose to use a dynamic or static cache. By default,
the lookup cache remains static and does not change during the session. With a
dynamic cache, the Informatica Server inserts rows into the cache during the
session. Informatica recommends that you cache the target table as the lookup.
This enables you to look up values in the target and insert them if they do not
exist.
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