Test Your PostgreSQL IS NULL Operator Knowledge with This Quiz

Progress

True / False

In PostgreSQL, the IS NULL operator is used to check if a value is NULL.

True False

The IS NULL operator in PostgreSQL checks if a column's value is NULL.

True / False

The expression NULL = NULL in PostgreSQL evaluates to TRUE.

True False

In PostgreSQL, NULL represents an unknown value, so NULL = NULL evaluates to FALSE. Instead, use IS NULL to check for NULL values.

True / False

In PostgreSQL, the IS NOT NULL operator is used to check if a value is not NULL.

True False

The IS NOT NULL operator checks if a column's value is not NULL.

True / False

In PostgreSQL, the IS NULL condition can be used in WHERE clauses to filter rows with NULL values.

True False

The IS NULL condition is commonly used in WHERE clauses to filter out rows that have NULL values in a specific column.

True / False

PostgreSQL treats empty strings and NULL as equivalent in IS NULL checks.

True False

PostgreSQL treats empty strings ('') and NULL as different. An empty string is a valid value, whereas NULL represents the absence of a value.

True / False

In PostgreSQL, using COALESCE(column_name, 'default_value') IS NULL will never evaluate to TRUE.

True False

COALESCE returns the first non-NULL value. If 'default_value' is provided, the result will never be NULL.

True / False

In PostgreSQL, using the IS DISTINCT FROM clause can be an alternative to IS NULL checks for handling NULL values.

True False

IS DISTINCT FROM treats NULL values as distinct from non-NULL values, providing a reliable way to compare NULLs and non-NULLs.

True / False

In PostgreSQL, you can create a partial index that only includes rows where a column is NULL using WHERE column IS NULL.

True False

Partial indexes can be created in PostgreSQL to include only rows that satisfy a specific condition, such as column IS NULL.

True / False

PostgreSQL allows using IS NULL in JOIN conditions to filter out rows with NULL values in the joined columns.

True False

IS NULL can be used in JOIN conditions to exclude rows with NULL values in the joined columns.

Q10

True / False

In PostgreSQL, the expression CASE WHEN column IS NULL THEN 'Yes' ELSE 'No' END can be used to replace NULL values with a specified string.

True False

The CASE expression in PostgreSQL can be used to check if a column is NULL and return a specified string, effectively replacing NULL values in the result set.

Q11

Single Choice

What does the IS NULL operator check in PostgreSQL?

If a value is equal to zero If a value is empty If a value is NULLIf a value is greater than zero

The IS NULL operator in PostgreSQL checks whether a value is NULL, meaning it has no value.

Q12

Single Choice

Given the SQL query:

SQL Code

SELECT * FROM employees WHERE salary IS NULL;
What does this query return?

All rows where the salary is zero All rows where the salary is NULL All rows where the salary is greater than zeroAll rows where the salary is not NULL

The query selects all rows where the salary column has a NULL value in PostgreSQL.

Q13

Single Choice

Which of the following statements will return rows where the column age is NULL in PostgreSQL?

SELECT * FROM persons WHERE age = 0; SELECT * FROM persons WHERE age = ''; SELECT * FROM persons WHERE age IS NULL;SELECT * FROM persons WHERE age IS NOT NULL;

The IS NULL operator in PostgreSQL checks for NULL values in the age column.

Q14

Single Choice

Consider the table orders with a column delivery_date. Which query will return orders with no scheduled delivery date in PostgreSQL?

SELECT * FROM orders WHERE delivery_date = '0000-00-00'; SELECT * FROM orders WHERE delivery_date = ''; SELECT * FROM orders WHERE delivery_date IS NULL;SELECT * FROM orders WHERE delivery_date IS NOT NULL;

The query using IS NULL returns orders where delivery_date has no assigned value (NULL) in PostgreSQL.

Q15

Single Choice

Given the following SQL:

SQL Code

SELECT COUNT(*) FROM products WHERE discontinued IS NULL;
What does this query count?

All products that are discontinued All products that are not discontinued All products with a NULL discontinued statusAll products with a non-NULL discontinued status

The query counts all rows in the products table where the discontinued column is NULL in PostgreSQL.

Q16

Single Choice

How can you select all rows from a table users where the last_login column has never been set (is NULL) in PostgreSQL?

SELECT * FROM users WHERE last_login = ''; SELECT * FROM users WHERE last_login = '0000-00-00'; SELECT * FROM users WHERE last_login IS NULL;SELECT * FROM users WHERE last_login IS NOT NULL;

The IS NULL operator is used in PostgreSQL to select rows where last_login has no value assigned.

Q17

Single Choice

In PostgreSQL, which of the following queries will correctly identify rows where the expiration_date column is NULL and the status is 'active'?

SELECT * FROM sessions WHERE expiration_date = NULL AND status = 'active'; SELECT * FROM sessions WHERE expiration_date IS NULL AND status = 'active'; SELECT * FROM sessions WHERE expiration_date IS NOT NULL AND status = 'active';SELECT * FROM sessions WHERE expiration_date = '' AND status = 'active';

The correct syntax to check for NULL values in PostgreSQL is IS NULL, not = NULL.

Q18

Single Choice

Which SQL statement will return all employees from the employee table where both termination_date and resignation_date are NULL in PostgreSQL?

SELECT * FROM employee WHERE termination_date = NULL AND resignation_date = NULL; SELECT * FROM employee WHERE termination_date IS NULL AND resignation_date IS NULL; SELECT * FROM employee WHERE termination_date IS NOT NULL AND resignation_date IS NOT NULL;SELECT * FROM employee WHERE termination_date IS NOT NULL OR resignation_date IS NOT NULL;

The IS NULL operator is required in PostgreSQL to correctly identify rows where both termination_date and resignation_date have NULL values.

Q19

Single Choice

How would you select records from a PostgreSQL database where a JSON field data->>'status' is not set (NULL)?

SELECT * FROM events WHERE data->>'status' = NULL; SELECT * FROM events WHERE data->>'status' IS NULL; SELECT * FROM events WHERE data->>'status' = '';SELECT * FROM events WHERE data->>'status' IS NOT NULL;

In PostgreSQL, the IS NULL operator is used to check if a JSON field value is NULL.

Q20

Single Choice

Given a table contracts with columns contract_id, start_date, and end_date, write a query to find all contracts where the end_date is NULL but the start_date is set in PostgreSQL.

SELECT * FROM contracts WHERE start_date IS NOT NULL AND end_date IS NULL; SELECT * FROM contracts WHERE start_date IS NULL AND end_date = ''; SELECT * FROM contracts WHERE start_date IS NOT NULL AND end_date = NULL;SELECT * FROM contracts WHERE start_date IS NOT NULL AND end_date IS NOT NULL;

The correct query uses IS NULL to identify contracts where end_date has no value (NULL) and start_date is set (NOT NULL) in PostgreSQL.

Q21

Multiple Choice

Identify the SQL scripts that correctly use the IS NULL operator to filter rows with null values in PostgreSQL.

SELECT * FROM employees WHERE manager_id IS NULL; SELECT * FROM employees WHERE manager_id = NULL; SELECT * FROM employees WHERE manager_id IS NOT NULL;SELECT * FROM employees WHERE manager_id = 'NULL';

The IS NULL operator is used to filter rows where the specified column has a null value. The correct scripts will demonstrate how to use the IS NULL operator in PostgreSQL.

Q22

Multiple Choice

Select the SQL scripts that correctly use the IS NULL operator with string values in PostgreSQL.

SELECT * FROM customers WHERE email IS NULL; SELECT * FROM customers WHERE email = NULL; SELECT * FROM customers WHERE email IS NULL OR email = '';SELECT * FROM customers WHERE email = 'NULL';

The IS NULL operator can be used to filter rows where a string column has a null value. The correct scripts will demonstrate how to use the IS NULL operator with string values in PostgreSQL.

Q23

Multiple Choice

Determine the SQL scripts that correctly use the IS NULL operator with subqueries in PostgreSQL.

SELECT * FROM employees WHERE department_id IS NULL AND department_id NOT IN (SELECT department_id FROM departments); SELECT * FROM employees WHERE department_id IS NULL; SELECT * FROM employees WHERE department_id IN (SELECT department_id FROM departments WHERE department_id IS NULL);SELECT * FROM employees WHERE department_id IS NULL AND EXISTS (SELECT 1 FROM departments WHERE departments.department_id = employees.department_id);

The IS NULL operator can be used with subqueries to filter rows where a value is null and the department does not exist. The correct scripts will demonstrate how to use the IS NULL operator with subqueries in PostgreSQL.

Q24

Multiple Choice

Identify the SQL scripts that correctly use the IS NULL operator with JOINs in PostgreSQL.

SELECT * FROM orders WHERE customer_id IS NULL AND NOT EXISTS (SELECT 1 FROM customers WHERE customers.customer_id = orders.customer_id); SELECT * FROM orders WHERE customer_id IS NULL; SELECT * FROM orders o LEFT JOIN customers c ON o.customer_id = c.customer_id WHERE o.customer_id IS NULL;SELECT * FROM orders WHERE customer_id IS NOT NULL AND EXISTS (SELECT 1 FROM customers WHERE customers.customer_id = orders.customer_id);

The IS NULL operator can be used with JOINs to filter rows based on null values in related tables. The correct scripts will demonstrate how to use the IS NULL operator with JOINs in PostgreSQL.

Q25

Multiple Choice

Select the SQL scripts that correctly use the IS NULL operator with multiple columns in PostgreSQL.

SELECT * FROM products WHERE category_id IS NULL AND supplier_id IS NULL; SELECT * FROM products WHERE category_id IS NULL OR supplier_id IS NULL; SELECT * FROM products WHERE category_id IS NULL AND supplier_id IS NOT NULL;SELECT * FROM products WHERE category_id IS NOT NULL AND supplier_id IS NOT NULL;

The IS NULL operator can be used with multiple columns to ensure that specific columns have null values. The correct scripts will demonstrate how to use the IS NULL operator with multiple columns in PostgreSQL.

Q26

Multiple Choice

Determine the SQL scripts that correctly use the IS NULL operator with window functions in PostgreSQL.

SELECT employee_id, department_id, RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) AS rank FROM employees WHERE salary IS NULL; SELECT employee_id, department_id, DENSE_RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) AS rank FROM employees WHERE salary IS NULL; SELECT employee_id, department_id, ROW_NUMBER() OVER (PARTITION BY department_id ORDER BY salary DESC) AS rank FROM employees WHERE salary IS NULL;SELECT employee_id, department_id, RANK() OVER (PARTITION BY department_id ORDER BY salary DESC) AS rank FROM employees WHERE salary IS NOT NULL;

The IS NULL operator can be used with window functions to filter and rank results based on null values. The correct scripts will demonstrate how to use the IS NULL operator with window functions in PostgreSQL.

Q27

Multiple Choice

Identify the SQL scripts that correctly use the IS NULL operator with EXISTS in PostgreSQL.

SELECT * FROM employees WHERE manager_id IS NULL AND NOT EXISTS (SELECT 1 FROM managers WHERE managers.manager_id = employees.manager_id); SELECT * FROM employees WHERE manager_id IS NULL; SELECT * FROM employees WHERE NOT EXISTS (SELECT 1 FROM managers WHERE managers.manager_id IS NULL AND managers.manager_id = employees.manager_id);SELECT * FROM employees WHERE manager_id IS NOT NULL AND EXISTS (SELECT 1 FROM managers WHERE managers.manager_id = employees.manager_id);

The IS NULL operator can be combined with EXISTS to filter rows where the value is null and does not exist in a related table. The correct scripts will demonstrate how to use the IS NULL operator with EXISTS in PostgreSQL.

Q28

Multiple Choice

Determine the SQL scripts that correctly use the IS NULL operator with UNION in PostgreSQL.

SELECT employee_id, email FROM employees WHERE email IS NULL UNION SELECT contractor_id, email FROM contractors WHERE email IS NULL; SELECT employee_id, email FROM employees WHERE email IS NULL UNION SELECT contractor_id, email FROM contractors WHERE email IS NOT NULL; SELECT employee_id, email FROM employees WHERE email IS NULL UNION ALL SELECT contractor_id, email FROM contractors WHERE email IS NULL;SELECT employee_id, email FROM employees WHERE email IS NOT NULL UNION SELECT contractor_id, email FROM contractors WHERE email IS NULL;

The IS NULL operator can be used with UNION to filter and combine results from multiple tables based on null values. The correct scripts will demonstrate how to use the IS NULL operator with UNION in PostgreSQL.

Q29

Multiple Choice

Identify the SQL scripts that correctly use the IS NULL operator with DISTINCT in PostgreSQL.

SELECT DISTINCT department_id FROM employees WHERE location_id IS NULL; SELECT DISTINCT department_id FROM employees WHERE location_id IS NULL AND department_id IS NULL; SELECT DISTINCT department_id FROM employees WHERE location_id IS NOT NULL;SELECT DISTINCT department_id FROM employees WHERE department_id IS NOT NULL AND location_id IS NULL;

The IS NULL operator can be used with DISTINCT to filter unique rows based on null values. The correct scripts will demonstrate how to use the IS NULL operator with DISTINCT in PostgreSQL.

Q30

Multiple Choice

Determine the SQL scripts that correctly use the IS NULL operator with LIMIT OFFSET in PostgreSQL.

SELECT * FROM orders WHERE order_date IS NULL ORDER BY order_id LIMIT 10 OFFSET 0; SELECT * FROM orders WHERE order_date IS NULL ORDER BY order_id LIMIT 10; SELECT * FROM orders WHERE order_date IS NULL ORDER BY order_id LIMIT 10 OFFSET 5;SELECT * FROM orders WHERE order_date IS NOT NULL ORDER BY order_id LIMIT 10 OFFSET 0;

The IS NULL operator can be used with LIMIT OFFSET to filter and paginate results based on null values. The correct scripts will demonstrate how to use the IS NULL operator with LIMIT OFFSET in PostgreSQL.

PostgreSQL Database Quiz Questions