FULL OUTER JOIN in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from both tables using a full outer join.

PostgreSQL

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

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AFULL OUTER JOIN

BINNER JOIN

CLEFT JOIN

DRIGHT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN which only returns matching rows.

Using LEFT JOIN or RIGHT JOIN which return only one side's unmatched rows.

The FULL OUTER JOIN returns all rows when there is a match in one of the tables. It combines the results of both left and right joins.

2fill in blank

medium

Complete the code to join orders and customers tables showing all orders and customers, matching by customer_id.

PostgreSQL

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

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ARIGHT JOIN

BFULL OUTER JOIN

CINNER JOIN

DLEFT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using INNER JOIN which excludes unmatched rows.

Using LEFT JOIN or RIGHT JOIN which exclude unmatched rows from one side.

Using FULL OUTER JOIN ensures all orders and all customers appear, even if some orders have no customer or some customers have no orders.

3fill in blank

hard

Fix the error in the join clause to correctly perform a full outer join between products and sales.

PostgreSQL

SELECT products.name, sales.amount FROM products [1] sales ON products.id = sales.product_id;

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AFULL OUTER JOIN

BLEFT OUTER JOIN

CFULL JOIN

DOUTER JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using OUTER JOIN without FULL, LEFT, or RIGHT.

Using LEFT OUTER JOIN which excludes unmatched rows from sales.

The correct syntax for a full outer join in PostgreSQL is FULL OUTER JOIN. Using just FULL JOIN also works but FULL OUTER JOIN is clearer and standard.

4fill in blank

hard

Fill both blanks to create a full outer join that shows all employees and their projects, matching by project_id.

PostgreSQL

SELECT employees.name, projects.title FROM employees [1] projects [2] employees.project_id = projects.id;

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AFULL OUTER JOIN

BON

CWHERE

DUSING

Attempts:

3 left

💡 Hint

Common Mistakes

Using WHERE instead of ON for join condition.

Using USING when column names differ.

The join type is FULL OUTER JOIN and the condition is specified with ON. The WHERE clause is not used for join conditions here, and USING requires matching column names.

5fill in blank

hard

Fill all three blanks to write a full outer join query that selects employee names, department names, and handles unmatched rows.

PostgreSQL

SELECT employees.name AS employee_name, departments.name AS department_name FROM employees [1] departments [2] employees.dept_id = departments.id [3] employees.name IS NULL OR departments.name IS NULL;

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

AFULL OUTER JOIN

BON

CWHERE

DLEFT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using LEFT JOIN which excludes unmatched rows from departments.

Using WHERE instead of ON for join condition.

The query uses FULL OUTER JOIN to include all rows. The join condition is specified with ON. The WHERE clause filters rows where either side is unmatched (NULL).