AVG() Aggregation With GROUP BY

Overview

AVG() returns the arithmetic mean of a numeric column. With GROUP BY, it summarizes a metric per bucket — here, the average production budget for each movie genre.

The Query

Step-by-Step Breakdown

1. AVG(budget_millions) averages budgets within each genre.
2. ROUND(..., 1) trims the mean to one decimal for readability.
3. COUNT(*) shows how many movies back each average.

Variations

Average salary per department:

Common Mistakes

• Averaging a count instead of a value. AVG(COUNT(*)) is illegal; you can't nest aggregates without a subquery.
• Letting NULLs skew intent. AVG ignores NULLs; if you need them as zero, wrap with COALESCE(col, 0) first.
• Forgetting GROUP BY. Without it you get one global average.