Exercises

SQL, Python, JavaScript exercises

82 checked exercises across 3 languages. SQL queries are compared with expected result sets on the sample database; Python and JavaScript programs run against multiple test inputs. Filter by topic, difficulty or progress. Your work stays in this browser.

SQL

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Look at the whole product catalogueEasy
The sales team wants to see everything we sell. Return every column of every row in the Products table.
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Just the names and pricesEasy
For a price list, return only the name and unit_price of every product — nothing else.
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Find the expensive productsEasy
Finance wants a list of products that cost more than 400. Return all columns for those products only.
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Who earns the most?Easy
Return the first_name, last_name and salary of every employee, with the highest earner first and the lowest earner last.
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The three priciest itemsEasy
Return the name and unit_price of just the three most expensive products, most expensive first.
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Which countries do we sell to?Easy
Marketing wants a de-duplicated list of the countries our customers are based in. Return each country exactly once, in a single column named country.
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Active engineers onlyEasy
HR needs the first_name and last_name of employees who are in department 10 and are currently active (active = 1). Both conditions must hold.
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Our best-tier customersEasy
Return the company and tier of every customer whose tier is either Gold or Platinum.
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Companies beginning with AMedium
Return the company name of every customer whose company name starts with the letter A.
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Who reports to nobody?Medium
Department heads have no manager, so their manager_id is empty. Return the first_name and last_name of every employee with no manager.
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How many customers do we have?Easy
Return a single row with a single column named total_customers holding the number of rows in the Customers table.
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Average salary, roundedEasy
Return the average employee salary rounded to the nearest whole number, in one column named avg_salary.
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Cheapest and dearestEasy
In one row, return the lowest unit_price as min_price and the highest as max_price from the Products table.
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Revenue actually shippedMedium
Cancelled and pending orders should not count as revenue. Return the sum of order_total for orders with status 'Shipped', in one column named shipped_revenue.
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Headcount per departmentMedium
Return each dept_id alongside the number of employees in it, with the count in a column named headcount.
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Biggest departments firstMedium
Return dept_id and headcount as before, but sort so the department with the most employees comes first.
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Only the multi-person departmentsMedium
Return dept_id and headcount for departments that contain more than two employees.
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Put a name to the departmentMedium
Employees only store a dept_id. Return each employee's first_name and last_name next to their dept_name by joining to the Departments table.
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Every department, even the quiet onesHard
Return every dept_name together with how many employees it has, named headcount. Departments with no employees at all must still appear, showing a count of 0.
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Label each order by sizeHard
Return order_id, order_total, and a column named size_band that reads 'Large' when order_total is 8000 or more, 'Medium' when it is at least 3000 but under 8000, and 'Small' otherwise.
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Better paid than averageMedium
Return the first_name, last_name and salary of every employee earning more than the company-wide average salary.
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Customers with a shipped orderMedium
Every customer has ordered something, but not every order ships. Return the company name of each customer who has had at least one order reach 'Shipped' status.
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Customers still waitingMedium
Now the exact opposite: return the company name of each customer who has never had an order ship — everything they ordered is still pending or was cancelled.
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Name the managerHard
Return each employee's first_name alongside their manager's first_name in a column named manager_name. Employees with no manager should be left out.
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One combined contact listMedium
Build a single two-column list of everyone we deal with. Return each employee's first_name and each customer's contact under a shared column named person_name, plus a column named source containing 'Employee' or 'Customer' as appropriate.
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Revenue by product categoryHard
Return each product category alongside the total order_total it has generated from shipped orders only, in a column named category_revenue, highest revenue first.
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Who is closing the deals?Hard
Return the first_name and last_name of each employee together with how many orders they handled, in a column named orders_handled, counting shipped orders only, and listing the busiest employee first. Only include employees who handled at least one shipped order.
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Big spendersHard
Return company and the total spend as total_spent for every customer whose combined order_total across all their orders exceeds 10000, largest spender first.
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Label the price bandsEasy
Marketing wants each product labelled. Return name, unit_price, and a column called price_label that says premium for products costing 500 or more and standard for everything else.
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Support levels by tierEasy
Support triages customers by tier. Return company, tier, and support_level: Platinum customers get 'Top priority', Gold customers get 'Standard support', and everyone else gets 'Self-serve'.
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One-row status reportMedium
Management wants the order pipeline on a single row: three columns named shipped, pending and cancelled, each counting the orders with that status.
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Revenue won and lostHard
For each employee who has handled orders, return first_name, shipped_revenue (total order_total of their Shipped orders) and cancelled_revenue (total of their Cancelled orders), highest shipped_revenue first.
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Mailing labelsEasy
HR needs mailing labels: a single column full_name (first name, a space, last name) plus email, for every employee, alphabetical by full_name.
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Case-insensitive searchEasy
A colleague types 'an' into the customer search box and expects every company whose name contains those two letters, whether they are stored in upper or lower case - so 'Andes' counts as well as 'Meridian'. Return company.
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Strip the domainMedium
For the Engineering department (dept_id 10), return each employee's email and a column mailbox holding the email with '@example.com' removed.
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The longest product namesMedium
The catalogue layout breaks on long names. Return name and name_length for every product whose name is 18 characters or longer.
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Who reports to whomMedium
List every employee's first_name alongside reports_to - their manager's first name, or the text 'No manager' for employees at the top of the tree.
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Orders by monthMedium
How does order volume spread across the year? Return order_month (the month number from order_date) and orders (how many orders that month), earliest month first.
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Big orders, with namesMedium
Define a CTE called big_orders that selects orders with order_total above 3000, then return order_id, company and order_total for those orders.
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Well-paid departmentsHard
Using a CTE that computes each department's average salary, return dept_name and avg_salary for the departments whose average exceeds 100000.
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Two CTEs, one reportHard
Build a per-salesperson report using two CTEs: one counting each employee's Shipped orders, one totalling each employee's revenue across all orders. Return first_name, shipped_orders and revenue, highest revenue first.
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Category revenue reportHard
The quarterly report needs revenue by product category, ignoring cancelled orders: return category, orders (count) and revenue (sum of order_total), biggest revenue first.
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Python

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JavaScript

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