Why CASE expressions are needed in SQL - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

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

SQL

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 wrong age value like 21 or 16 changes the classification incorrectly.

Forgetting to use '>=' causes wrong results.

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

2fill in blank

medium

Complete the code to assign 'Pass' if score is 50 or more, otherwise 'Fail'.

SQL

SELECT student, CASE WHEN score >= [1] THEN 'Pass' ELSE 'Fail' END AS result FROM exams;

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

A40

B50

C60

D70

Attempts:

3 left

💡 Hint

Common Mistakes

Using 40 or 60 changes pass/fail results incorrectly.

Not using '>=' causes wrong classification.

The passing score is 50, so the CASE expression uses 50 to decide.

3fill in blank

hard

Fix the error in the CASE expression to categorize salary as 'High' if above 70000, else 'Low'.

SQL

SELECT employee, CASE WHEN salary [1] 70000 THEN 'High' ELSE 'Low' END AS category FROM staff;

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

A<=

B<

C>=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using '>=' includes 70000 as 'High' which may not be intended.

To classify salary as 'High' when it is above 70000, use '>' operator.

4fill in blank

hard

Fill both blanks to classify temperature as 'Cold' if below 15, 'Warm' if between 15 and 25, else 'Hot'.

SQL

SELECT city, CASE WHEN temp < [1] THEN 'Cold' WHEN temp <= [2] THEN 'Warm' ELSE 'Hot' END AS weather FROM forecast;

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

A15

B20

C25

D30

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing thresholds causes wrong weather classification.

Using wrong comparison operators changes results.

Temperature below 15 is 'Cold', up to 25 is 'Warm', else 'Hot'.

5fill in blank

hard

Fill all three blanks to assign grade: 'A' if score >= 90, 'B' if >= 75, else 'C'.

SQL

SELECT student, CASE WHEN score >= [1] THEN 'A' WHEN score >= [2] THEN 'B' ELSE [3] END AS grade FROM results;

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

A90

B75

C'C'

D'B'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong thresholds mixes grades.

Not quoting grade letters causes syntax errors.

Grades are assigned based on score thresholds: 90 for A, 75 for B, else C.