A label such as "out of stock" or "low" is not in the table. CASE makes it from the values in each row.

SELECT name, price,
       CASE
         WHEN price < 10 THEN 'budget'
         WHEN price < 30 THEN 'standard'
         ELSE 'premium'
       END AS band
FROM products;

CASE tests the WHEN conditions from top to bottom, for each row. It returns the THEN value of the first condition that is true, and stops.

• The order of the WHEN lines matters. Put the narrowest condition first.
• ELSE is optional. Without it, a row with no true WHEN gets NULL.
• END closes the CASE. Give the column a name with AS.
• A CASE is an expression. You can use it in the SELECT list, in WHERE and in ORDER BY.