Conditional logic with CASE

SQL's if/else — bucket and relabel values inline.

if/else, inline

CASE is SQL's conditional expression. It checks conditions top to bottom and returns the first match's value:

SELECT title, price,
       CASE WHEN price < 12 THEN 'budget'
            WHEN price < 20 THEN 'standard'
            ELSE 'premium' END AS band
FROM books;

It works anywhere an expression is allowed — SELECT, WHERE, ORDER BY, even inside an aggregate. There's also a short "simple" form: CASE status WHEN 'paid' THEN 1 ELSE 0 END.

Conditions are tested top to bottom and the first true one wins, so a book at 9.99 is labelled budget and never reaches the price < 20 branch. ELSE catches whatever is left.

CASE is an expression, not a filter: all ten books come back, each carrying one extra computed value.