How to combine conditions
Require both with AND
AND keeps a row only when both conditions are true.
SELECT *
FROM courses
WHERE level = 'beginner'
AND duration_minutes < 90;Allow either with OR
OR keeps a row when at least one condition is true.
SELECT *
FROM courses
WHERE level = 'beginner'
OR level = 'intermediate';Reverse with NOT
NOT negates a condition. Clear positive conditions are often easier to understand.
SELECT *
FROM courses
WHERE NOT archived;Use parentheses
AND is evaluated before OR. Parentheses make the intended grouping explicit and prevent subtle mistakes.
WHERE active = 1
AND (level = 'beginner' OR level = 'intermediate')