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In SSIS, what is the difference between output columns and external columns?
Answer
External columns represent the meta data of external data sources and output columns are used be data flow source adapters.
Explanation
Output columns are used by all data-flow source adapters and transformations. They are not used by destination adapters. Put simply, they represent the metadata of the data flowing out of the component. External columns represent the metadata of external data sources and destinations. As such, only source & destination adapters have external columns because these are the only components whose buffered pipeline data interacts with these external sources and destinations.
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