An Egress Column is a column that has a special meaning for a particular sink - either a foreign stream or foreign table. Egress columns are normally specific to a particular formatter or writer plugin.
Instead of being sent to the sink as part of the regular data record, the data in the egress column is handled in some other way. For example:
By convention, most egress column names start with SQLSTREAM_EGRESS.
For more information, see: