Test Your Oracle LEFT JOIN Knowledge with This SQL Quiz

Progress

True / False

In Oracle, a LEFT JOIN returns all rows from the left table and the matching rows from the right table.

True False

The LEFT JOIN returns all rows from the left table and the matching rows from the right table. If there is no match, NULL values are returned for columns from the right table.

True / False

In Oracle, if there are no matching rows in the right table, the result of a LEFT JOIN will still include all rows from the left table.

True False

If there are no matching rows in the right table, all rows from the left table will still be included, with NULL values for columns from the right table.

True / False

In Oracle, the LEFT JOIN is also known as the LEFT OUTER JOIN.

True False

The LEFT JOIN is synonymous with LEFT OUTER JOIN, and both terms can be used interchangeably.

True / False

In Oracle, you can use the ON clause in a LEFT JOIN to specify the join condition.

True False

The ON clause is used to specify the join condition for a LEFT JOIN, determining how the rows from the left and right tables are matched.

True / False

In Oracle, using LEFT JOIN can result in duplicate rows in the result set if there are multiple matches in the right table.

True False

If there are multiple matching rows in the right table for a single row in the left table, LEFT JOIN will produce duplicate rows in the result set.

True / False

In Oracle, the LEFT JOIN can be combined with the WHERE clause to further filter the joined results.

True False

The LEFT JOIN can be used in conjunction with the WHERE clause to apply additional filtering criteria to the joined result set.

True / False

In Oracle, using LEFT JOIN on large tables without proper indexing can lead to poor query performance.

True False

Without proper indexing, LEFT JOIN on large tables can result in slow query performance due to the need to compare many rows.

True / False

In Oracle, you can use LEFT JOIN with multiple tables in a single query.

True False

LEFT JOIN can be used with multiple tables in a single query, allowing for complex joins involving more than two tables.

True / False

In Oracle, LEFT JOIN can be used to include rows from the left table that do not have corresponding matches in the right table.

True False

LEFT JOIN ensures that all rows from the left table are included in the result set, even if there are no matching rows in the right table.

Q10

True / False

The Oracle Certified Professional (OCP) exam includes knowledge on using LEFT JOIN effectively, understanding its syntax, and optimizing its performance in complex SQL queries.

True False

The OCP certification covers advanced topics, including the effective use of LEFT JOIN, understanding its syntax, and optimizing its performance in complex SQL queries.

Q11

Single Choice

What does a LEFT JOIN do in ORACLE SQL?

Combines all rows from the right table, with matching rows from the left table Combines all rows from the left table, with matching rows from the right table Combines only the rows with matching values from both tablesCombines all rows from both tables, regardless of matching values

A LEFT JOIN returns all rows from the left table and the matched rows from the right table. If no match is found, NULL values are returned for columns from the right table.

Q12

Single Choice

In ORACLE SQL, what happens if there are no matching rows in the right table when using a LEFT JOIN?

The query returns no rows The query returns all rows from the right table The query returns NULL for the columns from the right tableThe query returns only the rows that have matches

If there are no matching rows in the right table, a LEFT JOIN returns NULL for the columns from the right table while still returning all rows from the left table.

Q13

Single Choice

Which of the following is a basic syntax for a LEFT JOIN in ORACLE SQL?

SELECT columns FROM table1 LEFT JOIN table2 ON table1.column = table2.column; SELECT columns FROM table1 RIGHT JOIN table2 ON table1.column = table2.column; SELECT columns FROM table1 FULL JOIN table2 ON table1.column = table2.column;SELECT columns FROM table1 INNER JOIN table2 ON table1.column = table2.column;

The correct syntax for a LEFT JOIN includes the LEFT JOIN keyword followed by the ON clause to specify the matching columns.

Q14

Single Choice

Given the following ORACLE SQL query:What will this query return?

SQL Code

SELECT e.employee_id, e.first_name, d.department_name
FROM employees e
LEFT JOIN departments d ON e.department_id = d.department_id;

All employees, with their department names if they exist Only employees who have a department assigned All departments, with their employee names if they existOnly departments that have employees assigned

The query performs a LEFT JOIN, which returns all rows from the employees table and the corresponding department names from the departments table, or NULL if there is no match.

Q15

Single Choice

In ORACLE SQL, which of the following scenarios is best suited for using a LEFT JOIN?

When you need to find matching rows between two tables and only return those rows When you need to combine all rows from both tables, regardless of matching values When you need to return all rows from the left table and only matching rows from the right tableWhen you need to delete rows from one table based on matching values in another table

A LEFT JOIN is used when you want to return all rows from the left table, even if there are no matching rows in the right table.

Q16

Single Choice

What will the following ORACLE SQL query return?

SQL Code

SELECT p.product_name, o.order_id
FROM products p
LEFT JOIN orders o ON p.product_id = o.product_id
WHERE o.order_date IS NULL;

Products that have been ordered Products that have never been ordered Orders that have no productsAll products and their orders

This query uses a LEFT JOIN to find all products, and the WHERE clause filters the result to include only those products that do not have a matching order (i.e., those with no orders).

Q17

Single Choice

Consider the following ORACLE SQL query:What will this query return?

SQL Code

SELECT e.employee_id, e.first_name, d.department_name
FROM employees e
LEFT JOIN departments d ON e.department_id = d.department_id
WHERE d.department_name IS NOT NULL;

All employees and their department names Only employees who belong to a department All departments and their employeesOnly departments without any employees

The WHERE clause filters out the NULL values from the department_name column, effectively returning only those employees who are assigned to a department.

Q18

Single Choice

Which of the following ORACLE SQL queries would correctly return all departments, including those without any employees, along with the total number of employees in each department?

SELECT d.department_name, COUNT(e.employee_id) AS employee_count FROM departments d LEFT JOIN employees e ON d.department_id = e.department_id GROUP BY d.department_name; SELECT d.department_name, COUNT(e.employee_id) AS employee_count FROM employees e LEFT JOIN departments d ON e.department_id = d.department_id GROUP BY d.department_name; SELECT d.department_name, COUNT(e.employee_id) AS employee_count FROM departments d RIGHT JOIN employees e ON d.department_id = e.department_id GROUP BY d.department_name;SELECT d.department_name, COUNT(e.employee_id) AS employee_count FROM departments d INNER JOIN employees e ON d.department_id = e.department_id GROUP BY d.department_name;

This query uses a LEFT JOIN to include all departments, including those without any employees, and counts the number of employees in each department.

Q19

Single Choice

In ORACLE SQL, what is the outcome of a LEFT JOIN followed by a WHERE clause condition that applies to a column from the right table?

The JOIN operation is ignored The condition is applied after the JOIN, potentially filtering out unmatched rows The condition is applied before the JOIN, affecting the JOIN resultThe query returns an error

In a LEFT JOIN, the WHERE clause is applied after the JOIN operation. If the WHERE condition checks for a column from the right table, it can filter out rows that were originally included in the JOIN result, especially if they are NULL.

Q20

Single Choice

Given the following ORACLE SQL query:What does this query accomplish?

SQL Code

SELECT p.project_name, e.employee_id, e.first_name
FROM projects p
LEFT JOIN project_assignments pa ON p.project_id = pa.project_id
LEFT JOIN employees e ON pa.employee_id = e.employee_id
WHERE e.employee_id IS NULL;

Lists all projects along with their assigned employees Lists all employees and their assigned projects Lists all projects that have no employees assignedLists all employees who are not assigned to any projects

This query uses LEFT JOINs to combine projects with their assigned employees and then filters the results to include only those projects that do not have any employees assigned.

Q21

Multiple Choice

Which SQL code snippet correctly demonstrates a basic use of LEFT JOIN to retrieve all employees and their respective department names in Oracle?

SQL Code

SELECT e.employee_id, e.first_name, d.department_name
FROM employees e
LEFT JOIN departments d ON e.department_id = d.department_id;

SELECT e.employee_id, e.first_name, d.department_name
FROM employees e
LEFT OUTER JOIN departments d ON e.department_id = d.department_id;

SELECT e.employee_id, d.department_name
FROM employees e
LEFT JOIN departments d ON e.department_id = d.department_id;

SELECT e.employee_id, e.first_name, d.department_name FROM employees e LEFT JOIN departments d ON e.department_id = d.department_id; SELECT e.employee_id, e.first_name, d.department_name FROM employees e LEFT OUTER JOIN departments d ON e.department_id = d.department_id; SELECT e.employee_id, d.department_name FROM employees e LEFT JOIN departments d ON e.department_id = d.department_id;SELECT e.employee_id, d.department_name FROM employees e JOIN departments d ON e.department_id = d.department_id;

Options A, B, and C correctly use LEFT JOIN to retrieve all employees and their respective department names. Option D is incorrect because it does not use the LEFT JOIN correctly.

Q22

Multiple Choice

Which SQL code snippet uses LEFT JOIN to find customers who have not placed any orders in Oracle?

SQL Code

SELECT c.customer_id, c.customer_name, o.order_id
FROM customers c
LEFT JOIN orders o ON c.customer_id = o.customer_id
WHERE o.order_id IS NULL;

SELECT c.customer_id, c.customer_name, o.order_id
FROM customers c
LEFT JOIN orders o ON c.customer_id = o.customer_id
WHERE o.order_id IS NULL;

SELECT c.customer_id, c.customer_name
FROM customers c
LEFT JOIN orders o ON c.customer_id = o.customer_id
WHERE o.order_id IS NULL;

SELECT c.customer_id, c.customer_name, o.order_id FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id WHERE o.order_id IS NULL; SELECT c.customer_id, c.customer_name, o.order_id FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id WHERE o.order_id IS NULL; SELECT c.customer_id, c.customer_name FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id WHERE o.order_id IS NULL;SELECT c.customer_id, c.customer_name FROM customers c JOIN orders o ON c.customer_id = o.customer_id WHERE o.order_id IS NULL;

Options A, B, and C correctly use LEFT JOIN to find customers who have not placed any orders. Option D is incorrect because it does not use the LEFT JOIN.

Q23

Multiple Choice

Which SQL code snippet demonstrates the use of LEFT JOIN to include all products and their respective order quantities, even if some products have no orders, in Oracle?

SQL Code

SELECT p.product_id, p.product_name, SUM(o.quantity) AS total_ordered
FROM products p
LEFT JOIN order_items o ON p.product_id = o.product_id
GROUP BY p.product_id, p.product_name;

SELECT p.product_id, p.product_name, COALESCE(SUM(o.quantity), 0) AS total_ordered
FROM products p
LEFT JOIN order_items o ON p.product_id = o.product_id
GROUP BY p.product_id, p.product_name;

SELECT p.product_id, p.product_name
FROM products p
LEFT JOIN order_items o ON p.product_id = o.product_id;

SELECT p.product_id, p.product_name, SUM(o.quantity) AS total_ordered FROM products p LEFT JOIN order_items o ON p.product_id = o.product_id GROUP BY p.product_id, p.product_name; SELECT p.product_id, p.product_name, COALESCE(SUM(o.quantity), 0) AS total_ordered FROM products p LEFT JOIN order_items o ON p.product_id = o.product_id GROUP BY p.product_id, p.product_name; SELECT p.product_id, p.product_name FROM products p LEFT JOIN order_items o ON p.product_id = o.product_id;SELECT p.product_id, p.product_name FROM products p JOIN order_items o ON p.product_id = o.product_id;

Options A and B correctly use LEFT JOIN to include all products and their respective order quantities, even if some products have no orders. Option C is incorrect because it does not summarize the order quantities, and Option D is incorrect because it does not join the tables correctly.

Q24

Multiple Choice

Which SQL code snippet demonstrates the use of LEFT JOIN to retrieve employees and their corresponding manager names, including those without a manager, in Oracle?

SQL Code

SELECT e1.employee_id, e1.first_name AS employee_name, e2.first_name AS manager_name
FROM employees e1
LEFT JOIN employees e2 ON e1.manager_id = e2.employee_id;

SELECT e.employee_id, e.first_name, m.first_name AS manager_name
FROM employees e
LEFT JOIN employees m ON e.manager_id = m.employee_id;

SELECT e.employee_id, e.first_name AS employee_name, m.first_name AS manager_name
FROM employees e
LEFT OUTER JOIN employees m ON e.manager_id = m.employee_id;

SELECT e1.employee_id, e1.first_name AS employee_name, e2.first_name AS manager_name FROM employees e1 LEFT JOIN employees e2 ON e1.manager_id = e2.employee_id; SELECT e.employee_id, e.first_name, m.first_name AS manager_name FROM employees e LEFT JOIN employees m ON e.manager_id = m.employee_id; SELECT e.employee_id, e.first_name AS employee_name, m.first_name AS manager_name FROM employees e LEFT OUTER JOIN employees m ON e.manager_id = m.employee_id;SELECT e.employee_id, e.first_name, m.first_name AS manager_name FROM employees e JOIN employees m ON e.manager_id = m.employee_id;

Options A, B, and C correctly use LEFT JOIN to retrieve employees and their corresponding manager names, including those without a manager. Option D is incorrect because it does not use the LEFT JOIN.

Q25

Multiple Choice

Which SQL code snippet demonstrates the use of LEFT JOIN to retrieve all categories and the total number of products in each category, including categories without products, in Oracle?

SQL Code

SELECT c.category_name, COUNT(p.product_id) AS num_products
FROM categories c
LEFT JOIN products p ON c.category_id = p.category_id
GROUP BY c.category_name;

SELECT c.category_name, COUNT(p.product_id) AS num_products
FROM categories c
LEFT JOIN products p ON c.category_id = p.category_id
GROUP BY c.category_name
HAVING COUNT(p.product_id) >= 0;

SELECT c.category_name, COALESCE(COUNT(p.product_id), 0) AS num_products
FROM categories c
LEFT JOIN products p ON c.category_id = p.category_id
GROUP BY c.category_name;

SELECT c.category_name, COUNT(p.product_id) AS num_products FROM categories c LEFT JOIN products p ON c.category_id = p.category_id GROUP BY c.category_name; SELECT c.category_name, COUNT(p.product_id) AS num_products FROM categories c LEFT JOIN products p ON c.category_id = p.category_id GROUP BY c.category_name HAVING COUNT(p.product_id) >= 0; SELECT c.category_name, COALESCE(COUNT(p.product_id), 0) AS num_products FROM categories c LEFT JOIN products p ON c.category_id = p.category_id GROUP BY c.category_name;SELECT c.category_name FROM categories c LEFT JOIN products p ON c.category_id = p.category_id;

Options A, B, and C correctly use LEFT JOIN to retrieve all categories and the total number of products in each category, including categories without products. Option D is incorrect because it does not group the results by category_name.

Q26

Multiple Choice

Which SQL code snippet demonstrates advanced use of LEFT JOIN to retrieve orders and their corresponding customer names, including orders without customer information, in Oracle?

SQL Code

SELECT o.order_id, o.order_date, c.customer_name
FROM orders o
LEFT JOIN customers c ON o.customer_id = c.customer_id;

SELECT o.order_id, o.order_date, c.customer_name
FROM orders o
LEFT OUTER JOIN customers c ON o.customer_id = c.customer_id;

SELECT o.order_id, o.order_date, c.customer_name
FROM orders o
LEFT JOIN customers c ON o.customer_id = c.customer_id
ORDER BY o.order_date DESC;

SELECT o.order_id, o.order_date, c.customer_name FROM orders o LEFT JOIN customers c ON o.customer_id = c.customer_id; SELECT o.order_id, o.order_date, c.customer_name FROM orders o LEFT OUTER JOIN customers c ON o.customer_id = c.customer_id; SELECT o.order_id, o.order_date, c.customer_name FROM orders o LEFT JOIN customers c ON o.customer_id = c.customer_id ORDER BY o.order_date DESC;SELECT o.order_id, o.order_date FROM orders o WHERE o.customer_id IS NOT NULL;

Options A, B, and C correctly demonstrate advanced use of LEFT JOIN to retrieve orders and their corresponding customer names, including orders without customer information. Option D is incorrect because it does not join the tables correctly.

Q27

Multiple Choice

Which SQL code snippet demonstrates the use of LEFT JOIN to generate a report of sales regions and the total sales amounts, including regions with no sales, in Oracle?

SQL Code

SELECT r.region_name, SUM(s.sales_amount) AS total_sales
FROM regions r
LEFT JOIN sales s ON r.region_id = s.region_id
GROUP BY r.region_name;

SELECT r.region_name, SUM(s.sales_amount) AS total_sales
FROM regions r
LEFT JOIN sales s ON r.region_id = s.region_id
GROUP BY r.region_name
HAVING SUM(s.sales_amount) >= 0;

SELECT r.region_name, COALESCE(SUM(s.sales_amount), 0) AS total_sales
FROM regions r
LEFT JOIN sales s ON r.region_id = s.region_id
GROUP BY r.region_name;

SELECT r.region_name, SUM(s.sales_amount) AS total_sales FROM regions r LEFT JOIN sales s ON r.region_id = s.region_id GROUP BY r.region_name; SELECT r.region_name, SUM(s.sales_amount) AS total_sales FROM regions r LEFT JOIN sales s ON r.region_id = s.region_id GROUP BY r.region_name HAVING SUM(s.sales_amount) >= 0; SELECT r.region_name, COALESCE(SUM(s.sales_amount), 0) AS total_sales FROM regions r LEFT JOIN sales s ON r.region_id = s.region_id GROUP BY r.region_name;SELECT r.region_name FROM regions r LEFT JOIN sales s ON r.region_id = s.region_id;

Options A, B, and C correctly use LEFT JOIN to generate a report of sales regions and the total sales amounts, including regions with no sales. Option D is incorrect because it does not group the results by region_name.

Q28

Multiple Choice

Which SQL code snippet demonstrates the use of LEFT JOIN to find all departments and their respective employee counts, including departments with no employees, in Oracle?

SQL Code

SELECT d.department_name, COUNT(e.employee_id) AS num_employees
FROM departments d
LEFT JOIN employees e ON d.department_id = e.department_id
GROUP BY d.department_name;

SELECT d.department_name, COUNT(e.employee_id) AS num_employees
FROM departments d
LEFT JOIN employees e ON d.department_id = e.department_id
GROUP BY d.department_name
HAVING COUNT(e.employee_id) >= 0;

SELECT d.department_name, COALESCE(COUNT(e.employee_id), 0) AS num_employees
FROM departments d
LEFT JOIN employees e ON d.department_id = e.department_id
GROUP BY d.department_name;

SELECT d.department_name, COUNT(e.employee_id) AS num_employees FROM departments d LEFT JOIN employees e ON d.department_id = e.department_id GROUP BY d.department_name; SELECT d.department_name, COUNT(e.employee_id) AS num_employees FROM departments d LEFT JOIN employees e ON d.department_id = e.department_id GROUP BY d.department_name HAVING COUNT(e.employee_id) >= 0; SELECT d.department_name, COALESCE(COUNT(e.employee_id), 0) AS num_employees FROM departments d LEFT JOIN employees e ON d.department_id = e.department_id GROUP BY d.department_name;SELECT d.department_name FROM departments d LEFT JOIN employees e ON d.department_id = e.department_id;

Options A, B, and C correctly use LEFT JOIN to find all departments and their respective employee counts, including departments with no employees. Option D is incorrect because it does not join the tables correctly.

Q29

Multiple Choice

Which SQL code snippet demonstrates certification-level use of LEFT JOIN to generate a detailed report of customers and their last order dates, including customers without orders, in Oracle?

SQL Code

SELECT c.customer_id, c.customer_name, MAX(o.order_date) AS last_order_date
FROM customers c
LEFT JOIN orders o ON c.customer_id = o.customer_id
GROUP BY c.customer_id, c.customer_name;

SELECT c.customer_id, c.customer_name, MAX(o.order_date) AS last_order_date
FROM customers c
LEFT JOIN orders o ON c.customer_id = o.customer_id
GROUP BY c.customer_id, c.customer_name
HAVING MAX(o.order_date) IS NOT NULL;

SELECT c.customer_id, c.customer_name, COALESCE(MAX(o.order_date), 'No Orders') AS last_order_date
FROM customers c
LEFT JOIN orders o ON c.customer_id = o.customer_id
GROUP BY c.customer_id, c.customer_name;

SELECT c.customer_id, c.customer_name, MAX(o.order_date) AS last_order_date FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id GROUP BY c.customer_id, c.customer_name; SELECT c.customer_id, c.customer_name, MAX(o.order_date) AS last_order_date FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id GROUP BY c.customer_id, c.customer_name HAVING MAX(o.order_date) IS NOT NULL; SELECT c.customer_id, c.customer_name, COALESCE(MAX(o.order_date), 'No Orders') AS last_order_date FROM customers c LEFT JOIN orders o ON c.customer_id = o.customer_id GROUP BY c.customer_id, c.customer_name;SELECT c.customer_id, c.customer_name FROM customers c JOIN orders o ON c.customer_id = o.customer_id;

Options A, B, and C correctly demonstrate certification-level use of LEFT JOIN to generate a detailed report of customers and their last order dates, including customers without orders. Option D is incorrect because it does not join the tables correctly.

Q30

Multiple Choice

Which SQL code snippet demonstrates the use of LEFT JOIN to create a comprehensive list of all products and their corresponding supplier names, including products without suppliers, in Oracle?

SQL Code

SELECT p.product_name, s.supplier_name
FROM products p
LEFT JOIN suppliers s ON p.supplier_id = s.supplier_id;

SELECT p.product_name, s.supplier_name
FROM products p
LEFT OUTER JOIN suppliers s ON p.supplier_id = s.supplier_id;

SELECT p.product_name, COALESCE(s.supplier_name, 'No Supplier') AS supplier_name
FROM products p
LEFT JOIN suppliers s ON p.supplier_id = s.supplier_id;

SELECT p.product_name, s.supplier_name FROM products p LEFT JOIN suppliers s ON p.supplier_id = s.supplier_id; SELECT p.product_name, s.supplier_name FROM products p LEFT OUTER JOIN suppliers s ON p.supplier_id = s.supplier_id; SELECT p.product_name, COALESCE(s.supplier_name, 'No Supplier') AS supplier_name FROM products p LEFT JOIN suppliers s ON p.supplier_id = s.supplier_id;SELECT p.product_name FROM products p JOIN suppliers s ON p.supplier_id = s.supplier_id;

Options A, B, and C correctly use LEFT JOIN to create a comprehensive list of all products and their corresponding supplier names, including products without suppliers. Option D is incorrect because it does not include the supplier_name in the SELECT statement.

Oracle Database Quiz Questions