NULLIF function behavior in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return NULL if the two values are equal.

PostgreSQL

SELECT NULLIF(5, [1]);

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

A3

B7

C5

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a value different from 5 will return the first value instead of NULL.

The NULLIF function returns NULL if both arguments are equal. Here, 5 equals 5, so the result is NULL.

2fill in blank

medium

Complete the code to return the first value when the two values are different.

PostgreSQL

SELECT NULLIF('apple', [1]);

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A'orange'

B'apple'

C'apple '

D'APPLE'

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing the same string will return NULL instead of the first value.

NULLIF returns the first value if the two values are different. 'apple' and 'orange' are different, so it returns 'apple'.

3fill in blank

hard

Fix the error in the code to correctly use NULLIF with a column named score.

PostgreSQL

SELECT NULLIF(score, [1]) FROM results;

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Ascore

B'score'

CNULL

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around column names causes the function to compare to a string, not the column value.

To compare the column score to itself, use the column name without quotes. Using quotes treats it as a string literal.

4fill in blank

hard

Fill both blanks to return NULL if age equals 18, otherwise return age.

PostgreSQL

SELECT NULLIF([1], [2]) AS result FROM users;

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Aage

B18

C'18'

Duser_age

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around 18 makes it a string, which may not match the numeric column.

NULLIF compares the first argument to the second. Using age and 18 (number) correctly returns NULL if age is 18.

5fill in blank

hard

Fill all three blanks to return status in uppercase if status equals 'active', else return status.

PostgreSQL

SELECT COALESCE(NULLIF([1], [2]), [3]) AS status_check FROM accounts;

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Astatus

B'active'

CUPPER(status)

DLOWER(status)

Attempts:

3 left

💡 Hint

Common Mistakes

Using LOWER instead of UPPER changes the output case incorrectly.

Not quoting 'active' treats it as a column, causing errors.

NULLIF returns NULL if status equals 'active'. COALESCE then returns the uppercase status if NULLIF returns NULL.