Often I want to categorize by something that isn’t a column:

person 1: I want to count children/adults/teenagers but there’s no column for that!

person 2: no problem! jut categorize people based on age!

CASE is how to write an if statement in SQL. Here’s the syntax:

CASE
  WHEN <condition>        THEN <result>
  WHEN <other-condition>  THEN <result>
  ...
  ELSE <result>
END

example:

Here’s how to categorize people into age ranges!

SELECT first_name, age, CASE
  WHEN age < 13  THEN 'child'
  WHEN age < 20  THEN 'teenager'
  ELSE 'adult' END AS age_range
FROM people

(returns first THEN where the condition matches)

people:

result: