Lesson 19 / 37 · Joins

Joins chain left to right, one step each

Three joins are three steps. Each takes everything the previous step produced and pairs it with the next table. Watch the row count change at every step.

The query

SELECT c.name, p.name AS product, i.qty
FROM customers c
JOIN orders o ON o.customer_id = c.id
JOIN order_items i ON i.order_id = o.id
JOIN products p ON p.id = i.product_id
WHERE o.status = 'paid'

Try AND i.qty > 1 in WHERE: a filter can test a column of any joined table, and 2 rows remain.

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