Test Your MySQL NULL vs NOT NULL Knowledge with This Quiz

Progress

Single Choice

Which keyword is used to specify that a column can have no value in MySQL?

NOT NULL NULL EMPTYNone of the above

The NULL keyword is used to specify that a column can have no value.

Single Choice

What is the default value of a column if no value is specified and the column is defined as NULL in MySQL?

NULL NOT NULL 0"

If a column is defined as NULL and no value is specified, it defaults to NULL.

Single Choice

In MySQL, which clause is used to ensure a column must always have a value?

NOT NULL DEFAULT UNIQUENull

The NOT NULL clause ensures that a column must always have a value and cannot be left empty.

Single Choice

What will be the result of the following MySQL query: SELECT IFNULL(NULL, 'Value');?

NULL Value ErrorNone of the above

The IFNULL function returns the second argument if the first argument is NULL.

Single Choice

How do you modify a column to allow NULL values in MySQL?

ALTER TABLE table_name MODIFY column_name ALLOW NULL; ALTER TABLE table_name CHANGE column_name column_name TYPE NULL; ALTER TABLE table_name MODIFY column_name NULL;ALTER TABLE table_name ALTER column_name NULL;

The correct syntax to modify a column to allow NULL values is ALTER TABLE table_name MODIFY column_name NULL;.

Single Choice

In MySQL, which function can be used to replace NULL values with a specified value?

COALESCE NULLIF NULLISNull

The COALESCE function returns the first non-NULL value from the list of arguments.

Single Choice

Which of the following statements is true about NULL values in MySQL?

NULL is equivalent to an empty string. NULL can be used in arithmetic operations. NULL is not equal to NULL.NULL values can be compared using the = operator.

In SQL, NULL is not equal to NULL. To check for NULL, use IS NULL or IS NOT NULL.

Single Choice

What is the result of the following MySQL query: SELECT COUNT(*) FROM table WHERE column IS NULL;?

Number of rows where the column has NULL values Number of rows where the column has non-NULL values Total number of rows in the tableError in query

The query counts the number of rows where the specified column has NULL values.

Single Choice

Which MySQL function is used to return NULL if the two expressions are equal?

IFNULL COALESCE NULLIFISNULL

The NULLIF function returns NULL if the two expressions are equal, otherwise, it returns the first expression.

Q10

Single Choice

Which of the following SQL queries correctly finds rows where the email column is NOT NULL in a MySQL database?

SELECT * FROM users WHERE email IS NOT NULL; SELECT * FROM users WHERE email != NULL; SELECT * FROM users WHERE email <> NULL;SELECT * FROM users WHERE email IS NOT EMPTY;

The correct query to find rows where the email column is not NULL is SELECT * FROM users WHERE email IS NOT NULL;.

Q11

True / False

In MySQL, a column defined as NOT NULL can never contain a NULL value.

True False

The NOT NULL constraint enforces that a column cannot have a NULL value.

Q12

True / False

In MySQL, you can use the IS NULL keyword to check if a value is NULL.

True False

The IS NULL keyword is used to check whether a column contains a NULL value.

Q13

True / False

In MySQL, NULL is the same as an empty string or zero.

True False

NULL represents the absence of any value, while an empty string or zero is an actual value.

Q14

True / False

In MySQL, using IS NOT NULL in a query filters out all NULL values.

True False

The IS NOT NULL keyword is used to exclude NULL values from the result set.

Q15

True / False

MySQL's COUNT(*) function counts NULL values in a column.

True False

COUNT(*) counts all rows in a table, including those with NULL values.

Q16

True / False

In MySQL, the COALESCE function returns the first non-NULL value from its arguments.

True False

The COALESCE function returns the first non-NULL value in the list of arguments provided.

Q17

True / False

In MySQL, the IFNULL function can be used to replace NULL values with a specified value.

True False

The IFNULL function takes two arguments and returns the first argument if it is not NULL, otherwise it returns the second argument.

Q18

True / False

In MySQL, an index can be created on columns that contain NULL values.

True False

MySQL allows creating indexes on columns that contain NULL values.

Q19

True / False

In MySQL, the NULLIF function returns NULL if the two arguments are equal, otherwise it returns the first argument.

True False

The NULLIF function compares two expressions and returns NULL if they are equal; otherwise, it returns the first expression.

Q20

True / False

In MySQL, a column with a default value of NULL will automatically be assigned a value if no value is provided during an insert operation.

True False

If a column has a default value of NULL, it will be assigned a NULL value if no value is provided during an insert operation, not automatically assigned a non-NULL value.

Q21

Multiple Choice

Identify the correct SQL statement to create a table with a column that allows NULL values.

SQL Code

CREATE TABLE employees (
 employee_id INT PRIMARY KEY,
 middle_name VARCHAR(50) NULL
);

CREATE TABLE employees ( employee_id INT PRIMARY KEY, middle_name VARCHAR(50) NULL ); CREATE TABLE employees ( employee_id INT PRIMARY KEY, middle_name VARCHAR(50) NOT NULL ); CREATE TABLE employees ( employee_id INT PRIMARY KEY, middle_name VARCHAR(50) );CREATE TABLE employees ( employee_id INT PRIMARY KEY, middle_name VARCHAR(50) DEFAULT NULL );

In MySQL, columns are allowed to have NULL values by default, but explicitly specifying NULL makes it clear that the column can store NULL values.

Q22

Multiple Choice

Select the correct SQL statement to modify a column to NOT allow NULL values.

SQL Code

ALTER TABLE orders
MODIFY COLUMN order_date DATE NOT NULL;

ALTER TABLE orders MODIFY COLUMN order_date DATE NOT NULL; ALTER TABLE orders ALTER COLUMN order_date DATE NOT NULL; ALTER TABLE orders CHANGE COLUMN order_date DATE NOT NULL;ALTER TABLE orders MODIFY COLUMN order_date DATE NULL;

The MODIFY COLUMN clause is used to change a column’s properties, including adding a NOT NULL constraint to prevent NULL values.

Q23

Multiple Choice

Determine the correct SQL statement to create a table with a column that must have a value.

SQL Code

CREATE TABLE products (
 product_id INT PRIMARY KEY,
 product_name VARCHAR(100) NOT NULL
);

CREATE TABLE products ( product_id INT PRIMARY KEY, product_name VARCHAR(100) NOT NULL ); CREATE TABLE products ( product_id INT PRIMARY KEY, product_name VARCHAR(100) NULL ); CREATE TABLE products ( product_id INT PRIMARY KEY, product_name VARCHAR(100) );CREATE TABLE products ( product_id INT PRIMARY KEY, product_name VARCHAR(100) DEFAULT 'Unknown' );

The NOT NULL constraint ensures that the column must always have a value; it cannot be left empty (NULL).

Q24

Multiple Choice

Which SQL statement correctly sets a column's default value to NULL?

SQL Code

ALTER TABLE users
MODIFY COLUMN last_login TIMESTAMP NULL DEFAULT NULL;

ALTER TABLE users MODIFY COLUMN last_login TIMESTAMP NULL DEFAULT NULL; ALTER TABLE users MODIFY COLUMN last_login TIMESTAMP DEFAULT NULL; ALTER TABLE users CHANGE COLUMN last_login TIMESTAMP DEFAULT NULL;ALTER TABLE users ALTER COLUMN last_login TIMESTAMP NULL DEFAULT NULL;

Specifying NULL as the default value ensures that if no value is provided during insertion, the column will store a NULL value.

Q25

Multiple Choice

Choose the correct SQL statement to check if a column allows NULL values.

SQL Code

SHOW COLUMNS FROM customers
WHERE Field = 'email';

SHOW COLUMNS FROM customers WHERE Field = 'email'; DESCRIBE customers WHERE Field = 'email'; SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'customers' AND COLUMN_NAME = 'email';SHOW FULL COLUMNS FROM customers WHERE Field = 'email';

The SHOW COLUMNS statement retrieves information about the columns, including whether they allow NULL values.

Q26

Multiple Choice

Identify the correct SQL statement to create a table with multiple NOT NULL columns.

SQL Code

CREATE TABLE orders (
 order_id INT PRIMARY KEY,
 customer_id INT NOT NULL,
 order_date DATE NOT NULL,
 total_amount DECIMAL(10, 2) NOT NULL
);

CREATE TABLE orders ( order_id INT PRIMARY KEY, customer_id INT NOT NULL, order_date DATE NOT NULL, total_amount DECIMAL(10, 2) NOT NULL ); CREATE TABLE orders ( order_id INT PRIMARY KEY, customer_id INT, order_date DATE, total_amount DECIMAL(10, 2) NOT NULL ); CREATE TABLE orders ( order_id INT PRIMARY KEY, customer_id INT NULL, order_date DATE NULL, total_amount DECIMAL(10, 2) NOT NULL );CREATE TABLE orders ( order_id INT PRIMARY KEY, customer_id INT NOT NULL, order_date DATE DEFAULT CURRENT_DATE, total_amount DECIMAL(10, 2) NOT NULL );

All specified columns in this table are marked as NOT NULL, ensuring that each must have a value when inserting a new row.

Q27

Multiple Choice

Select the correct SQL statement to modify a table by adding a NOT NULL constraint to an existing column.

SQL Code

ALTER TABLE inventory
MODIFY COLUMN stock_quantity INT NOT NULL;

ALTER TABLE inventory MODIFY COLUMN stock_quantity INT NOT NULL; ALTER TABLE inventory ADD CONSTRAINT NOT NULL FOR COLUMN stock_quantity; ALTER TABLE inventory CHANGE COLUMN stock_quantity INT NOT NULL;ALTER TABLE inventory ALTER COLUMN stock_quantity INT NOT NULL;

Adding a NOT NULL constraint to an existing column ensures that the column must have a value and cannot be NULL.

Q28

Multiple Choice

Determine the correct SQL statement to drop a NOT NULL constraint from a column.

SQL Code

ALTER TABLE employees
MODIFY COLUMN middle_name VARCHAR(50) NULL;

ALTER TABLE employees MODIFY COLUMN middle_name VARCHAR(50) NULL; ALTER TABLE employees ALTER COLUMN middle_name DROP NOT NULL; ALTER TABLE employees CHANGE COLUMN middle_name VARCHAR(50) NULL;ALTER TABLE employees DROP CONSTRAINT NOT NULL ON COLUMN middle_name;

To drop the NOT NULL constraint, you must modify the column to allow NULL values by specifying NULL in the ALTER TABLE statement.

Q29

Multiple Choice

Which SQL statement correctly creates a table with a default value of NULL for a column?

SQL Code

CREATE TABLE contacts (
 contact_id INT PRIMARY KEY,
 email VARCHAR(100) DEFAULT NULL
);

CREATE TABLE contacts ( contact_id INT PRIMARY KEY, email VARCHAR(100) DEFAULT NULL ); CREATE TABLE contacts ( contact_id INT PRIMARY KEY, email VARCHAR(100) NULL DEFAULT NULL ); CREATE TABLE contacts ( contact_id INT PRIMARY KEY, email VARCHAR(100) NULL );CREATE TABLE contacts ( contact_id INT PRIMARY KEY, email VARCHAR(100) DEFAULT 'N/A' );

By specifying DEFAULT NULL, the email column will have a default value of NULL if no value is provided during insertion.

Q30

Multiple Choice

Choose the correct SQL statement to enforce a NOT NULL constraint on a column during table creation.

SQL Code

CREATE TABLE payments (
 payment_id INT PRIMARY KEY,
 amount DECIMAL(10, 2) NOT NULL,
 payment_date DATE NOT NULL
);

CREATE TABLE payments ( payment_id INT PRIMARY KEY, amount DECIMAL(10, 2) NOT NULL, payment_date DATE NOT NULL ); CREATE TABLE payments ( payment_id INT PRIMARY KEY, amount DECIMAL(10, 2), payment_date DATE NOT NULL ); CREATE TABLE payments ( payment_id INT PRIMARY KEY, amount DECIMAL(10, 2) DEFAULT 0, payment_date DATE NOT NULL );CREATE TABLE payments ( payment_id INT PRIMARY KEY, amount DECIMAL(10, 2) NOT NULL, payment_date DATE );

The NOT NULL constraint ensures that both the amount and payment_date columns must always have a value when inserting a new row.

MySQL Database Quiz Questions