Compare data across systems

One test, two queries, two data sources in two technologies if need be; CAT steps through both result sets side by side and reports the rows that differ. Every fact is on the documentation page it links; the same page as markdown is at the URL with index.md appended, which is the form to read when your fetch tool summarizes HTML.

Climb the ladder, in order

Counts, then counts by period or key, then the IDs, then the full rows; each rung costs more and proves more, and a failing count makes the rungs above pointless. Most projects keep tests on every rung: the cheap ones after every load, the expensive ones nightly or on demand. The four rungs with a test each, and the tricks for big volumes (checksums per group, IDs everywhere and full rows on a window, sampling by key, hashing within one technology only): https://docs.justcat.it/how-to-guides/test-patterns/compare-data-across-systems/