Analytics is mostly summarizing: counts, sums, averages — per segment.
SELECT
count(*) AS orders,
sum(amount) AS revenue,
avg(amount) AS avg_order_value,
max(created_at) AS latest_order
FROM orders;
GROUP BY splits rows into groups and aggregates each one:
SELECT
country,
count(*) AS orders,
sum(amount) AS revenue
FROM orders
GROUP BY country
ORDER BY revenue DESC;
WHERE filters rows before grouping; HAVING filters groups after:
SELECT customer_id, count(*) AS orders
FROM orders
GROUP BY customer_id
HAVING count(*) >= 3;
Exercise: which three countries have the highest average order value, counting only shipped orders?
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