MySQL + SQL · Lesson 99
BEFORE and AFTER Triggers
Trigger Timing
A trigger fires either BEFORE or AFTER the event. BEFORE can change/validate the data; AFTER reacts once it is done.
BEFORE Trigger
CREATE TRIGGER before_marks_insert
BEFORE INSERT ON students
FOR EACH ROW
SET NEW.marks = LEAST(NEW.marks, 100); -- cap marks at 100BEFORE lets you fix/validate the value before it is stored.
AFTER Trigger
AFTER triggers run once the row is committed — used for logging, updating totals in another table, etc.
Summary
- BEFORE = validate/modify data before saving.
- AFTER = react after the change (logging, summaries).