SQL Latest Row Per Key
Return the newest status or event for each item.
What this solves
Get the current status for every production order. This pattern is useful when the business question is clear but a generic tutorial is too abstract.
The rule
Rank rows by time inside each key and keep rank 1.
WITH x AS (SELECT *, ROW_NUMBER() OVER(PARTITION BY PO ORDER BY EventTime DESC) rn FROM Events) SELECT * FROM x WHERE rn=1;Real-work checklist
- Define the business key and expected grain before writing the formula, query or markup.
- Test the pattern on a small known sample where you can verify the answer manually.
- Check missing values, duplicates and data types before trusting a large result.
- Scale to the real file or database only after the logic is proven.
Common mistake
MAX(EventTime) alone does not automatically return the other columns from the same row.