SQL Aggregate Functions: COUNT, SUM, MIN, MAX, and AVG Explained

A table can contain hundreds, thousands, or millions of rows. Aggregate functions help you compress those rows into numbers you can understand quickly: counts, totals, extremes, and averages.

In SQL for Files, you can practice aggregates on sample sales data or run the same ideas against local files in your browser with DuckDB WASM.

COUNT tells you how many rows match a question. SUM adds numeric values such as revenue, quantity, or cost.

SELECT
  COUNT(*) AS sale_count,
  SUM(amount) AS total_amount
FROM sales
WHERE region = 'West';

MIN finds the smallest value, MAX finds the largest value, and AVG calculates the mean. Together, they give you a quick profile of a numeric column.

SELECT
  MIN(amount) AS smallest_sale,
  MAX(amount) AS largest_sale,
  AVG(amount) AS average_sale
FROM sales;

A plain aggregate query without GROUP BY usually returns one row. That one row represents a summary of all matching rows after WHERE filtering has been applied.

This is why aggregates are so useful for dashboards: one query can return the headline numbers your reader needs first.

1. Use COUNT to count matching rows.
2. Use SUM to total sales amounts.
3. Combine COUNT and SUM for compact reporting.
4. Finish with MIN, MAX, and AVG to profile values.