Average Ignoring NULL Scores

Problem

Return class_id and avg_score from scores grouped by class_id. NULL scores should be ignored by AVG. Sort by class_id.

Why This Matters

SQL NULLs are a constant interview trap. AVG ignores NULL automatically, but COUNT(*) does not.

Schema

scores(class_id INTEGER, student_id INTEGER, score REAL)

Examples

Constraints

• Return the exact structure requested.
• Handle the edge cases mentioned in the prompt.
• Prefer clear logic over clever one-liners.