How the join engine matches rows in SQL - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from the two tables joined on the customer_id.

SQL

SELECT * FROM orders JOIN customers ON orders.[1] = customers.customer_id;

Drag options to blanks, or click blank then click option'

Aorder_date

Border_id

Ccustomer_id

Dproduct_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using order_id instead of customer_id in the join condition.

Joining on columns that don't relate the two tables.

The join condition must match the customer_id column from orders to customers to combine related rows.

2fill in blank

medium

Complete the code to perform an INNER JOIN between employees and departments on department_id.

SQL

SELECT employees.name, departments.name FROM employees [1] JOIN departments ON employees.department_id = departments.department_id;

Drag options to blanks, or click blank then click option'

AINNER

BRIGHT

CLEFT

DFULL

Attempts:

3 left

💡 Hint

Common Mistakes

Using LEFT JOIN which includes all employees even without a department.

Using FULL JOIN which includes unmatched rows from both tables.

INNER JOIN returns rows where the join condition matches in both tables.

3fill in blank

hard

Fix the error in the join condition to correctly match orders with customers.

SQL

SELECT * FROM orders JOIN customers ON orders.[1] = customers.[2];

Drag options to blanks, or click blank then click option'

Aorder_id

Bcustomer_id

Cproduct_id

Dorder_date

Attempts:

3 left

💡 Hint

Common Mistakes

Using order_id or product_id in the join condition causing no matches.

Using different columns on each side of the join condition.

The join condition must use the customer_id column from both tables to match related rows.

4fill in blank

hard

Fill both blanks to select employee names and their department names using a join.

SQL

SELECT employees.[1], departments.[2] FROM employees JOIN departments ON employees.department_id = departments.department_id;

Drag options to blanks, or click blank then click option'

Aname

Bid

Dlocation

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting department id instead of name.

Selecting employee id instead of name.

We select the employee's name and the department's name columns to show both.

5fill in blank

hard

Fill all three blanks to select order id, customer name, and order date from joined tables.

SQL

SELECT orders.[1], customers.[2], orders.[3] FROM orders JOIN customers ON orders.customer_id = customers.customer_id;

Drag options to blanks, or click blank then click option'

Aorder_id

Bname

Corder_date

Dcustomer_id

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting customer_id instead of customer name.

Mixing columns from wrong tables.

We select order_id and order_date from orders, and name from customers to show order details with customer names.