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2026-07-29 16:01
Database

Inner Join Tables

QueryValidateMedium
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What you will learn

  • INNER JOIN drops rows where the right table has no match — verify row count, not just shape, to catch silent data loss
  • Join on indexed columns only — a query that works on 100 rows may table-scan at 10M. EXPLAIN before trusting test speed
  • Test NULL in join columns: INNER JOIN silently excludes them, LEFT JOIN includes with NULL — know which you need

Description

Get all orders with user names.

Test Scenario

-- Your query:
SELECT o.id, u.name, o.status, o.total
FROM orders o
INNER JOIN users u ON o.user_id = u.id;

-- Expected: 5 orders with user names
-- Sample: 1 | John Doe | completed | 1349.98

Testing Tips

  • •INNER JOIN returns matching rows only
  • •ON specifies join condition
  • •Use table aliases for clarity
// Playwright API Testing - Database
import { test, expect } from '@playwright/test';


test('Database query via API', async ({ request }) => {
  const response = await request.post('/api/database/query', {
    data: {
      sql: 'SELECT * FROM users WHERE id = ?',
      params: [1]
    }
  });


  expect(response.ok()).toBeTruthy();
  const { rows } = await response.json();
  expect(rows.length).toBeGreaterThan(0);
});

Challenge ID: sql-inner-join

2 frameworks available