How to use COUNT, SUM, AVG

Count rows

COUNT(*) counts rows. COUNT(column) counts only rows where that column is not NULL.

SELECT COUNT(*) AS course_count
FROM courses;

Add values

SUM totals non-NULL numeric values and returns NULL when no input rows exist.

SELECT SUM(duration_minutes) AS total_minutes
FROM courses;

Calculate an average

AVG averages non-NULL numeric values. Cast or round according to the precision your result needs.

SELECT AVG(duration_minutes) AS average_minutes
FROM courses;

Combine with filters

WHERE filters input rows before aggregation. Use GROUP BY when you need one summary per category.