CASE Expressions

The CASE expression allows you to add conditional logic to SQL queries.

It works like IF or SWITCH statements in programming languages. You can return different values depending on conditions.

The CASE expression evaluates conditions in order and returns the first matching result.

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CASE
  WHEN condition1 THEN result1
  WHEN condition2 THEN result2
  ...
  ELSE default_result
END

CASE can be used inside SELECT, ORDER BY, WHERE, and even window functions.

Let's use the CodeFriends dataset to categorize users based on how far they've progressed in a course.

course_progress

We can use CASE to assign each user a label:

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SELECT user_id,
  course_name,
  progress_percent,
  CASE
    WHEN progress_percent = 100 THEN 'Completed'
    WHEN progress_percent >= 75 THEN 'Almost done'
    WHEN progress_percent >= 50 THEN 'Halfway'
    ELSE 'Just started'
  END AS completion_status
FROM course_progress;

Result:

Use CASE when you need to apply conditional rules directly inside your query. It’s ideal for:

• Categorizing or labeling data based on conditions
• Replacing values dynamically
• Embedding simple logic without extra tables or code

This makes CASE especially useful in reporting, dashboards, and analytical queries where flexible data presentation is required.