Why NULL is not a value in SQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select rows where the column 'age' is NULL.

SQL

SELECT * FROM users WHERE age [1] NULL;

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

A<>

B!=

C=

DIS

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' to compare with NULL, which always returns false.

In SQL, NULL is not a value, so you must use IS or IS NOT to check for NULL.

2fill in blank

medium

Complete the code to select rows where 'salary' is NOT NULL.

SQL

SELECT * FROM employees WHERE salary [1] NULL;

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

A=

B<>

CIS NOT

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' or '<>' to check for NOT NULL, which does not work correctly.

To check that a column is not NULL, use IS NOT NULL in SQL.

3fill in blank

hard

Fix the error in the query to find rows where 'score' is NULL.

SQL

SELECT * FROM results WHERE score [1] NULL;

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

ALIKE

BIS

C=

DIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' or 'LIKE' to compare with NULL.

Use IS NULL to check for NULL values, not '=' or other operators.

4fill in blank

hard

Fill both blanks to select rows where 'date' is NULL or 'status' is NOT NULL.

SQL

SELECT * FROM orders WHERE date [1] NULL OR status [2] NULL;

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

AIS

BIS NOT

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' or '!=' to check for NULL or NOT NULL.

Use IS NULL to check for NULL and IS NOT NULL to check for NOT NULL.

5fill in blank

hard

Fill all three blanks to select rows where 'price' is NULL, 'quantity' is NOT NULL, and 'discount' equals 0.

SQL

SELECT * FROM sales WHERE price [1] NULL AND quantity [2] NULL AND discount [3] 0;

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

AIS

BIS NOT

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' to check for NULL or '!=' to check for NOT NULL.

Use IS NULL for NULL, IS NOT NULL for NOT NULL, and '=' for exact value comparison.