CASE WHEN expression in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the CASE WHEN expression in SQL?

The CASE WHEN expression lets you perform conditional logic inside SQL queries. It works like an if-else statement to return different values based on conditions.

beginner

Write the basic syntax of a CASE WHEN expression.

The syntax is:<br>

CASE<br>  WHEN condition1 THEN result1<br>  WHEN condition2 THEN result2<br>  ELSE default_result<br>END

beginner

Can CASE WHEN be used in the SELECT clause? Give an example.

Yes, it can. For example:<br>

SELECT name,<br>  CASE WHEN score >= 60 THEN 'Pass'<br>       ELSE 'Fail'<br>  END AS result<br>FROM students;

intermediate

What happens if none of the WHEN conditions are true and there is no ELSE clause?

If no WHEN condition matches and there is no ELSE, the CASE expression returns NULL.

intermediate

How can CASE WHEN improve readability compared to nested IF statements?

CASE WHEN organizes multiple conditions clearly in one block, making queries easier to read and maintain than many nested IF functions.

What does the CASE WHEN expression return if a condition is true?

A The result specified after THEN

B NULL

C The ELSE result

D An error

When a WHEN condition is true, CASE returns the value after THEN.

Which clause is optional in a CASE WHEN expression?

A WHEN

B END

C THEN

D ELSE

The ELSE clause is optional. If omitted and no conditions match, CASE returns NULL.

Where can you use CASE WHEN in a SQL query?

A In SELECT, WHERE, ORDER BY, and more

B Only in SELECT clause

C Only in WHERE clause

D Only in JOIN conditions

CASE WHEN can be used in many parts of a query like SELECT, WHERE, ORDER BY, etc.

What is the correct way to end a CASE WHEN expression?

A FINISH

B END

C STOP

D DONE

Every CASE expression must end with the keyword END.

If you want to assign grades based on scores using CASE WHEN, which is a valid condition?

A WHEN grade THEN score

B WHEN score = 'A' THEN 90

C WHEN score > 90 THEN 'A'

D WHEN THEN score > 90

Conditions in WHEN must be logical expressions like score > 90.

Explain how the CASE WHEN expression works in SQL and give a simple example.

Think of it like an if-else chain inside a query.

Describe a situation where using CASE WHEN improves a SQL query compared to multiple separate queries.

Consider grading students or categorizing data in one query.