Parentheses and NOT

When a condition has both AND and OR, it matters which of them goes first. Say you want the sports or racing games that cost less than $20, and you write:

SELECT title, genre, price
FROM games
WHERE genre = 'Sports' OR genre = 'Racing' AND price < 20
ORDER BY title;

Goal Rush costs $50, so why is it there? AND goes before OR, just as multiplication goes before addition in math. SQLite first joins genre = 'Racing' AND price < 20, and only then adds OR genre = 'Sports'. So the query has found the racing games under $20 and all the sports games, whatever their price.

To make OR go first, put it in parentheses, as in math:

SELECT title, genre, price
FROM games
WHERE (genre = 'Sports' OR genre = 'Racing') AND price < 20
ORDER BY title;

Now every game must be a sports or a racing game, and also cost less than $20. Whenever a condition mixes AND and OR, use parentheses: you won't have to remember which goes first, and whoever reads the query will see at once what you meant.

NOT in front of a condition turns it around: it's true where the condition is false, and the other way round. NOT price < 20 is the same as price >= 20. It's most useful in front of parentheses, where it turns around the whole condition inside them. The games that are neither sports nor racing games:

SELECT title, genre
FROM games
WHERE NOT (genre = 'Sports' OR genre = 'Racing')
ORDER BY title;

Without the parentheses, NOT would turn around only the first condition: NOT genre = 'Sports' OR genre = 'Racing' finds all the games that aren't sports games, the racing ones included.