Lesson 17 — Conditional UPDATE

UPDATE: change existing rows

UPDATE table SET column = value WHERE condition changes rows that match. The SET part can use the old value: SET price = price * 0.9 gives a 10% discount. After an UPDATE, cursor.rowcount tells you how many rows changed.

UPDATE staff SET salary = salary * 1.05 WHERE team = 'support'

Watch out: an UPDATE without WHERE changes every row in the table. Always write the WHERE first.

Why it matters: price changes, status updates and "mark as read" are all UPDATEs — and a missing WHERE is a classic production accident.