Tuesday, March 19, 2013

When do you use connected lookup and unconnected lookup?

Connected Lookup :
A connected Lookup transformation is part of the mapping data flow. With connected lookups, you can have multiple return values. That is, you can pass multiple values from the same row in the lookup table out of the Lookup transformation.
Common uses for connected lookups include:
  • Finding a name based on a number ex. Finding a Dname based on deptno
  • Finding a value based on a range of dates
  • Finding a value based on multiple conditions

Unconnected Lookup :
An unconnected Lookup transformation exists separate from the data flow in the mapping. You write an expression using the :LKP reference qualifier to call the lookup within another transformation.
Some common uses for unconnected lookups include:
  • Testing the results of a lookup in an expression
  • Filtering records based on the lookup results
  • Marking records for update based on the result of a lookup (for example, updating slowly changing dimension tables)
  • Calling the same lookup multiple times in one mapping

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