Why equals NULL fails in SQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if 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!=

CIS

D<>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' to compare with NULL

Using '<>' to compare with NULL

In SQL, to check if a value is NULL, you must use IS NULL. Using = NULL does not work because NULL means unknown.

2fill in blank

medium

Complete the code to find rows where 'score' is not NULL.

SQL

SELECT * FROM results WHERE score [1] NULL;

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

AIS NOT

B=

C!=

D<>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' or '<>' to check for NOT NULL

Using '=' instead of 'IS NOT'

To check for values that are not NULL, use IS NOT NULL. Other operators do not work with NULL.

3fill in blank

hard

Fix the error in the WHERE clause to correctly filter NULL values.

SQL

SELECT * FROM orders WHERE delivery_date [1] NULL;

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

A!=

BIS

C=

DLIKE

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' or '!=' with NULL

Using 'LIKE' with NULL

Use IS NULL to check for NULL values. Operators like '=' or '!=' do not work with NULL.

4fill in blank

hard

Fill both blanks to correctly filter rows where 'status' is NULL or not NULL.

SQL

SELECT * FROM tasks WHERE status [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 '!=' instead of IS or IS NOT

Mixing up IS and IS NOT

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

5fill in blank

hard

Fill all three blanks to create a query that selects rows where 'comment' is NULL, 'rating' is not NULL, and 'approved' equals 1.

SQL

SELECT * FROM feedback WHERE comment [1] NULL AND rating [2] NULL AND approved [3] 1;

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

AIS

BIS NOT

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' or '!=' to compare with NULL

Using IS or IS NOT for normal values

Use IS NULL to check for NULL, IS NOT NULL for not NULL, and = for normal value comparison.