Window Functions vs. GROUP BY: A Deep Dive

The Comparison

| Feature | GROUP BY | Window Function |

|---------|----------|-----------------|

| Rows returned | One per group | All original rows |

| Can access individual column values | No (unless aggregated or grouped) | Yes |

| Use case | Summary reports | Detailed reports with context |

| Performance | Generally faster for simple sums | Slightly more overhead |

**GROUP BY**: "What is the total sales per region?"

**Window Function**: "For each order, show its amount AND the region's total."

You can use both in the same query! GROUP BY the high-level summary, then use a window function on the grouped result.

*Day 71: Introduction to Query Optimization.*