14.4 Practice: Match Shipments to Hubs on Paper First

Why. Matching a few rows by hand first shows you exactly what a join should return. Then you can trust or question the SQL result.

What. On paper, you take each shipment, read its hub_id, and look for the same hub_id in hubs. You note three outcomes: one match, no match because the hub does not exist, and no match because the hub is missing.

How. List shipments with their hub_id, list hubs, and match them yourself before you run any join.

SELECT shipment_id, customer_id, hub_id
FROM shipments
ORDER BY shipment_id;

SELECT hub_id, hub_code, city
FROM hubs
ORDER BY hub_id;