Aggregate Functions

The five common ones

COUNT, SUM, AVG, MIN, MAX collapse many rows into a single summary value.

SELECT COUNT(*) AS total_orders,
       SUM(amount) AS revenue,
       AVG(amount) AS avg_order,
       MAX(amount) AS biggest
FROM orders;

Output:

total_orders | revenue | avg_order | biggest
3            | 4500.00 | 1500.00   | 2000.00

COUNT(*) vs COUNT(column)

COUNT(*) counts all rows; COUNT(column) skips rows where that column is NULL.

Quick check: Which counts only non-NULL values in a column?

• COUNT(*)
• COUNT(column_name)
• SUM(column_name)