Data engineering·Quality, tests and knowing it is wrong
before merging, you run both versions of the model and see that exactly nine hundred rows differ, all in one region.
Data diff
Also calledtable diff, output comparison
Comparing the output of a changed transformation against the current one, row by row. It converts 'I think this refactor is safe' into a list you can walk through, and it catches the accidental cross join that a row-count check would miss. It is expensive on large tables, which is why it is usually run on a sampled or single-partition basis, and that sampling has to be stated when the result is presented as evidence.