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2026-07-29 16:01
Database

Filter Aggregated Results

QueryValidateMedium
Try Interactive Demo

What you will learn

  • HAVING filters GROUPS (aggregates), WHERE filters ROWS — WHERE on an aggregate fails at parse time
  • Prune rows with WHERE first (cheap), then GROUP, then HAVING — reversing order kills performance at scale
  • HAVING references aggregate aliases (HAVING count > 5) — raw column expressions silently work in MySQL but not Postgres

Description

Find users who have placed more than 1 order.

Test Scenario

-- Your query:
SELECT u.name, COUNT(o.id) as order_count
FROM users u
JOIN orders o ON u.id = o.user_id
GROUP BY u.id, u.name
HAVING COUNT(o.id) > 1;

-- Expected: Users with multiple orders

Testing Tips

  • •HAVING filters after GROUP BY
  • •WHERE filters before GROUP BY
  • •Use HAVING with aggregate functions
// 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-having

2 frameworks available