CASE expression in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return 'Adult' if age is 18 or more, otherwise 'Minor'.

PostgreSQL

SELECT name, CASE WHEN age >= [1] THEN 'Adult' ELSE 'Minor' END AS status FROM people;

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

A18

B21

C16

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Using a number less than 18 will misclassify adults as minors.

Using '>' instead of '>=' excludes exactly 18 years old.

The CASE expression checks if age is 18 or more to classify as 'Adult'.

2fill in blank

medium

Complete the code to categorize scores: 90 or above as 'Excellent', else 'Good'.

PostgreSQL

SELECT student, CASE WHEN score >= [1] THEN 'Excellent' ELSE 'Good' END AS grade FROM results;

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A80

B85

C90

D95

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a lower number will mark too many as 'Excellent'.

Choosing a higher number excludes some who scored exactly 90.

The CASE expression uses 90 as the threshold for 'Excellent'.

3fill in blank

hard

Fix the error in the CASE expression to correctly assign 'Pass' if marks are 50 or more, else 'Fail'.

PostgreSQL

SELECT student, CASE WHEN marks [1] 50 THEN 'Pass' ELSE 'Fail' END AS result FROM exams;

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

A>

B>=

C<=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' excludes students with exactly 50 marks.

Using '<' or '<=' reverses the logic.

The '>=' operator includes 50 marks as passing.

4fill in blank

hard

Fill both blanks to classify temperature: 'Hot' if temp > 30, 'Warm' if temp > 20, else 'Cold'.

PostgreSQL

SELECT city, CASE WHEN temperature [1] 30 THEN 'Hot' WHEN temperature [2] 20 THEN 'Warm' ELSE 'Cold' END AS weather FROM forecast;

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

A>

B>=

C<=

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>=' includes boundary values incorrectly here.

Using '<=' or '<' reverses the logic.

Use '>' to check if temperature is greater than 30 for 'Hot' and greater than 20 for 'Warm'.

5fill in blank

hard

Fill all three blanks to create a CASE expression that returns 'A' for score >= 90, 'B' for score >= 80, else 'C'.

PostgreSQL

SELECT student, CASE WHEN score [1] 90 THEN 'A' WHEN score [2] 80 THEN 'B' ELSE [3] END AS grade FROM tests;

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

A>=

B>

C'C'

D'B'

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' excludes boundary scores.

Not quoting the ELSE result causes syntax errors.

The CASE uses '>=' to include boundary scores and returns 'C' as the else result.