Part 92: Window Functions vs GROUP BY: Deep Architectural Comparison
Understanding how rows pass through the database execution engine.
1. Key Differences
| Feature | GROUP BY |
Window Functions (OVER) |
|---|---|---|
| Output Row Count | Collapses N rows into 1 row per group | Keeps all original N rows |
| Execution Order | Executes before SELECT |
Executes during SELECT |
| Access to Other Rows | Only aggregated values available | Can read values from previous/next rows |
Key Takeaways
- Use
GROUP BYwhen you want a condensed summary. - Use Window Functions when you need row-level calculations alongside group metrics.
In Part 93, we master Ranking Functions: ROW_NUMBER(), RANK(), and DENSE_RANK()!