SQL in one afternoon

Most day-to-day SQL uses five clauses in a fixed order: SELECT, FROM, WHERE, GROUP BY and ORDER BY. Learn what each one does and you can answer a surprising number of business questions. Any free online SQL playground will run these examples.

A table to practise on

CREATE TABLE orders (id INT, region TEXT, amount NUMERIC, placed_on DATE);
INSERT INTO orders VALUES
  (1, 'North', 120, '2026-09-01'),
  (2, 'South', 80.5, '2026-09-02'),
  (3, 'North', 200, '2026-09-05'),
  (4, 'East', 55, '2026-09-05');

SELECT and FROM: which columns, from where

SELECT region, amount FROM orders;

WHERE: keep only some rows

SELECT * FROM orders WHERE amount > 100;

GROUP BY: summarise rows into groups

SELECT region, SUM(amount) AS revenue, COUNT(*) AS orders
FROM orders
GROUP BY region;

ORDER BY: sort the result

SELECT region, SUM(amount) AS revenue
FROM orders
GROUP BY region
ORDER BY revenue DESC;

The order SQL actually runs in

You write SELECT first, but the database works FROM, then WHERE, then GROUP BY, then SELECT, then ORDER BY. That's why you can't use a column alias like revenue inside WHERE: it doesn't exist yet at that stage. Use HAVING to filter after grouping.

SELECT region, SUM(amount) AS revenue
FROM orders
GROUP BY region
HAVING SUM(amount) > 100;

Next step: the Business Intelligence and Data Analytics program builds from these basics to modelling, dashboards and KPI design.