Joins in SQL in DBMS Theory - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from two tables using an INNER JOIN.

DBMS Theory

SELECT * FROM employees [1] departments ON employees.department_id = departments.id;

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

AINNER JOIN

BJOIN

CLEFT JOIN

DRIGHT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using LEFT JOIN instead of INNER JOIN returns unmatched rows from the left table.

Using JOIN alone may work but is less explicit than INNER JOIN.

The INNER JOIN keyword selects records that have matching values in both tables.

2fill in blank

medium

Complete the code to select all employees and their departments, including employees without a department.

DBMS Theory

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

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

AINNER JOIN

BLEFT JOIN

CRIGHT JOIN

DFULL JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes employees without departments.

Using RIGHT JOIN would keep all departments, not employees.

The LEFT JOIN returns all employees, even if they don't belong to a department.

3fill in blank

hard

Fix the error in the join type to include all records from both tables.

DBMS Theory

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

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AINNER JOIN

BLEFT JOIN

CFULL OUTER JOIN

DCROSS JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes unmatched rows.

Using CROSS JOIN produces a Cartesian product, not a join on keys.

FULL OUTER JOIN returns all records when there is a match in either left or right table.

4fill in blank

hard

Fill both blanks to select all customers and their orders, including customers without orders.

DBMS Theory

SELECT customers.name, orders.order_date FROM customers [1] orders ON customers.id [2] orders.customer_id;

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

ALEFT JOIN

B=

C!=

DRIGHT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using RIGHT JOIN would keep all orders, not customers.

Using != in ON condition breaks the join logic.

The LEFT JOIN keeps all customers, and the = operator matches customer IDs.

5fill in blank

hard

Fill all three blanks to create a query that selects product names and supplier names, including products without suppliers.

DBMS Theory

SELECT products.name, suppliers.name FROM products [1] suppliers ON products.supplier_id [2] suppliers.id WHERE suppliers.country [3] 'USA';

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

ALEFT JOIN

B=

DINNER JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN excludes products without suppliers.

Using != in ON or WHERE clauses breaks the intended logic.

LEFT JOIN includes all products, = matches supplier IDs, and = filters suppliers from USA.