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AVG() Aggregation With GROUP BY

Compute the average movie budget per genre using AVG() grouped by genre.

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

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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.

AVG ignores NULLs

Like other aggregates, AVG skips NULL rows rather than treating them as zero, which keeps the average honest.

Variations

Average salary per department:

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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.

Related examples

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Use HAVING to keep only departments whose average salary exceeds a threshold after aggregation.

Cite this resource

SQLSimplified. "AVG() Aggregation With GROUP BY Example". Available at: https://sqlsimplified.online/examples/group-by-average