MySQL Aggregate Functions: COUNT, SUM, AVG, MIN, MAX

Aggregate functions condense many rows into one number — the totals, averages, and counts that fill every business report. Mastering their NULL behaviour and DISTINCT variants prevents subtle reporting errors.

Key Points

• COUNT(*) counts rows; COUNT(col) skips NULLs — they differ!
• SUM and AVG ignore NULLs; use COALESCE(col, 0) to treat them as zero
• COUNT(DISTINCT customer_id) counts unique customers
• MIN/MAX work on dates and strings too, not just numbers
• Combine with GROUP BY for per-category summaries
• GROUP_CONCAT aggregates values into a single string list