10. MySQL Part 1: Install, Create, Insert and SELECT

10.8 Aggregate Functions, GROUP BY and HAVING

By Ravindra Bagale · Last updated: 27 September 2026

Aggregate functions anek rows varun ek uttar kaadhtat. GROUP BY rows gat-gat karto, HAVING gatanvar filter lavto.

SELECT COUNT(*) AS total_students FROM students;
SELECT COUNT(email) FROM students;                     -- ignores NULLs → 9
SELECT SUM(fees_paid), AVG(fees_paid), MIN(age), MAX(age) FROM students;

SELECT city, COUNT(*) AS students FROM students GROUP BY city;
SELECT city, SUM(fees_paid) AS total_fees FROM students
  GROUP BY city ORDER BY total_fees DESC;

SELECT city, COUNT(*) AS students FROM students
  GROUP BY city HAVING COUNT(*) >= 2;                  -- only cities with 2+ students

SELECT city, AVG(age) AS avg_age FROM students
  WHERE fees_paid > 0                                  -- filter rows first
  GROUP BY city
  HAVING AVG(age) > 23;                                -- then filter groups

Order of execution: FROM → WHERE → GROUP BY → HAVING → SELECT → ORDER BY → LIMIT.