Add Polybase Rejected Rows DMV
The REJECT_TYPE and REJECT_VALUE settings on a Polybase External Table are very useful for managing invalid data types, but they are very limited if you're using Polybase as a data loading mechanism. In order for this to be useful, we need visibility of which rows were rejected, even if it was within the tolerance.
I would suggest a generic system view that logged the failed row as an untyped string (or JSON/XML string if in the SQL engine rather than the Azure SQL Datawarehouse engine).
This would read something like:
reject_id, object_id, query_date, reject_string
The external table would have config along the lines of "REJECT_LOGGING" (true/false) and REJECT_RETENTION (hours/days etc)
SQL DW now supports reject row location where rows are written if they fail to load.