Aggregate Functions, GROUP BY, HAVING, and Reporting Queries

Why Aggregation Matters

Applications often need more than raw rows. Teams want totals, averages, maximum values, monthly counts, and grouped reports. MariaDB can calculate these efficiently close to the data, which reduces application-side loops and improves clarity.

Common Aggregate Functions

• COUNT() counts rows
• SUM() totals numeric values
• AVG() computes averages
• MIN() and MAX() find boundaries

SELECT COUNT(*) AS total_customers
FROM customers
WHERE status = 'ACTIVE';

Grouping by Meaningful Dimensions

SELECT
    order_status,
    COUNT(*) AS order_count
FROM orders
GROUP BY order_status;

Grouping lets you summarize by status, department, region, product category, month, assignee, or any other useful dimension. This is the basis of many management dashboards.

Filtering Aggregates with HAVING

SELECT
    customer_id,
    COUNT(*) AS total_orders
FROM orders
GROUP BY customer_id
HAVING COUNT(*) >= 5;

WHERE filters rows before grouping. HAVING filters grouped results after aggregation. Understanding that distinction prevents many beginner mistakes.