Could email be a unique key?
The team wants a unique key on employees.email. Check whether the current data allows it. Return one row with two numbers: the number of employees, and the number of distinct non-NULL email values. No email is NULL in this data, so if the two differ, some email is shared and the key would fail.
Rows can come back in any order. Column names do not matter; the values do.
Sample database: Company: departments, employees and orders
Three tables. departments (id, name, city). employees (id, name, email, dept_id, manager_id, salary, bonus, hire_date): dept_id and manager_id may be NULL, bonus may be NULL, hire_date is text in the form YYYY-MM-DD. orders (id, employee_id, customer, amount, status, order_date): employee_id is the sales rep (an employee id), amount may be NULL, status is DELIVERED, SHIPPED, PENDING or CANCELLED in capitals, and order_date is text in the form YYYY-MM-DD. Foreign keys are not enforced, so an order may point to an employee who does not exist.
| id | name | city |
|---|---|---|
| 1 | Engineering | Bengaluru |
| 2 | QA | Pune |
| 3 | Sales | Mumbai |
| 4 | HR | Pune |
| 5 | Support | Chennai |
| id | name | dept_id | manager_id | salary | bonus | hire_date | |
|---|---|---|---|---|---|---|---|
| 1 | Asha Rao | asha@shop.in | 1 | NULL | 150000 | 20000 | 2018-03-01 |
| 2 | Vikram Shah | vikram@shop.in | 1 | 1 | 95000 | NULL | 2020-07-15 |
| 3 | Neha Gupta | neha@shop.in | 2 | 1 | 82000 | 5000 | 2021-01-10 |
| 4 | Rohan Mehta | rohan@shop.in | 2 | 3 | 64000 | NULL | 2022-06-01 |
| 5 | Priya Nair | priya@shop.in | 2 | 3 | 64000 | 3000 | 2023-02-20 |
| 6 | Arjun Das | arjun@shop.in | 3 | 1 | 70000 | 15000 | 2019-11-05 |
| 7 | Kavya Iyer | kavya@shop.in | 3 | 6 | 52000 | NULL | 2024-01-08 |
| 8 | Imran Khan | imran@shop.in | 4 | 1 | 58000 | 2000 | 2020-09-30 |
| 9 | Sneha Patil | neha@shop.in | NULL | 1 | 47000 | NULL | 2025-04-14 |
| 10 | Dev Malhotra | dev@shop.in | 1 | 2 | 95000 | 8000 | 2022-12-01 |
| id | employee_id | customer | amount | status | order_date |
|---|---|---|---|---|---|
| 101 | 6 | Acme Ltd | 12000 | DELIVERED | 2026-01-05 |
| 102 | 6 | Bharat Traders | 4500 | CANCELLED | 2026-01-09 |
| 103 | 7 | Acme Ltd | 8000 | DELIVERED | 2026-02-11 |
| 104 | 7 | Cosmo Retail | 15000 | SHIPPED | 2026-02-20 |
| 105 | 6 | Delta Foods | 3000 | PENDING | 2026-03-02 |
| 106 | 7 | Bharat Traders | 9500 | DELIVERED | 2026-03-15 |
| 107 | 12 | Echo Stores | 7000 | DELIVERED | 2026-03-18 |
| 108 | 6 | Acme Ltd | NULL | PENDING | 2026-04-01 |
| 109 | 7 | Cosmo Retail | 15000 | SHIPPED | 2026-02-20 |
| 110 | 8 | Fresh Mart | 2500 | DELIVERED | 2026-04-10 |
Run shows your rows. Submit compares them with the expected rows.