CASE Expressions

The CASE expression lets you add conditional logic to your SQL queries.

It's like using if or switch statements in programming. You can return different values depending on conditions.

You can use CASE to add conditional logic to your SQL queries.

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

You can use CASE inside SELECT, ORDER BY, WHERE, and even inside 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:

With CASE, you can categorize or label data based on rules, replace values conditionally, and add logic directly into your queries without writing extra code.

It's especially useful in reporting, dashboards, and analysis tasks.