What is the difference between External Column vs an Output Column?

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I'm trying to learn SSIS and stuck on what exactly are External Columns and Output Columns? It seems like all that metadata could be stored in just one... unless there is another reason I'm not understanding. If someone could explain what each really is in clear language then maybe I could figure this out.

I've read explanation on this site. Read explanations on the MSDN site. Searched answers on Google. Read about this in a book titled "Professional Microsoft SQL Server 2014 Integration Services".

sql-server-data-tools etl ssis metadata sql-server
2 Answers

  • External Columns live outside of the environment you are working (Excel, text files, databases).

    Are SOURCES and DESTINATIONS.

  • Input Columns are columns inside the environment that go into an object (SOURCE, TRANSFORM or DESTINATION)

  • Output Columns are inside the environment that exit an object (SOURCE, TRANSFORM, or DESTINATION)

External Columns are initially converted to Input Columns a source object expects.

External Columns do not match [out of synch] means your source changed somehow. Usually a column name or a data type changed.

Similarly, Output Columns of a destination lead to External Columns.

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