NULL behavior in comparisons in SQL - Interactive Code Practice

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'

AIS

B=

C!=

D<>

Attempts:

3 left

💡 Hint

Common Mistakes

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

Forgetting that NULL is not equal to anything, even NULL.

In SQL, to check if a value is NULL, you must use IS NULL. Using '=' or '!=' does not work as expected with NULL.

2fill in blank

medium

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

SQL

SELECT * FROM results WHERE score [1] NULL;

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

A!=

BIS NOT

C=

D<>

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using '=' instead of 'IS NOT'.

To find rows where a column is not NULL, use IS NOT NULL. Other operators do not work correctly with NULL.

3fill in blank

hard

Fix the error in the WHERE clause to correctly filter rows where 'date' is NULL.

SQL

SELECT * FROM events WHERE date [1] NULL;

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

A=

BLIKE

CIS

DIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' to compare with NULL.

Using string matching operators like LIKE with NULL.

Only IS NULL correctly checks for NULL values in SQL. '=' causes errors or unexpected results.

4fill in blank

hard

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

SQL

SELECT * FROM tasks WHERE status [1] NULL OR priority [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 the order of NULL checks.

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 select rows where 'email' is NULL, 'phone' is NOT NULL, and 'address' is NULL.

SQL

SELECT * FROM contacts WHERE email [1] NULL AND phone [2] NULL AND address [3] NULL;

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

AIS

BIS NOT

C=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' or '!=' for NULL comparisons.

Using the wrong operator for NOT NULL checks.

Use IS NULL to check for NULL and IS NOT NULL to check for NOT NULL values in SQL.