Learn Three-Table JOINs: THE TOWER

THE TOWER is chapter 10, where joins go multi-table. The covert supply network spans three tables: SUPPLIERS (front companies), SHIPMENTS (cargo and weights), and DESTINATIONS (black sites and safe houses). SHIPMENTS carries both a SUPPLIER_ID and a DESTINATION_ID, so tracing a route means chaining two INNER JOINs in one query.

The missions build the trace one hop at a time: supplier to shipment first, then the full supplier-to-destination line, then a filtered weapons-only trail. Each stage returns live rows, and the server checks your result before the investigation advances.

Once two ON clauses feel natural, three or four stop being scary. The joins guide linked below has diagrams if you want them.

This is the shape of query you practice here, not the answer to any mission. The real stages come with their own data, objectives, and hints.

SELECT SUPPLIERS.COMPANY_NAME, DESTINATIONS.SITE_NAME
FROM SUPPLIERS
INNER JOIN SHIPMENTS ON SUPPLIERS.ID = SHIPMENTS.SUPPLIER_ID
INNER JOIN DESTINATIONS ON SHIPMENTS.DESTINATION_ID = DESTINATIONS.ID;

Free guides that pair well with this chapter:

• Common Table Expressions (CTEs) and Recursion
• SQL Joins Explained: INNER, LEFT, RIGHT, FULL