SQL triggers

Syntax:

CREATE TRIGGER trigger_name trigger_time trigger_event
ON table_name
FOR EACH ROW
BEGIN
...
END

Dropping trigger:

DROP TRIGGER table_name.trigger_name

Example 1:

CREATE TABLE account (acct_num INT, amount DECIMAL(10,2));

CREATE TRIGGER ins_sum BEFORE INSERT ON account FOR EACH ROW SET @sum = @sum + NEW.amount;

SET @sum = 0;
mysql> INSERT INTO account VALUES(137,14.98),(141,1937.50),(97,-100.00);
mysql> SELECT @sum AS 'Total amount inserted';

Example 2:

CREATE TRIGGER `tutorial`.`before_delete_carts`
    BEFORE DELETE ON `trigger_carts` FOR EACH ROW
    BEGIN
        DELETE FROM trigger_cart_items WHERE OLD.cart_id = cart_id;
    END

Example 3:

CREATE TRIGGER `after_update_cost`
    AFTER UPDATE ON `trigger_items_cost` FOR EACH ROW
    BEGIN
       UPDATE trigger_items
       SET price = (NEW.cost * 1.3)
       WHERE item_id = NEW.item_id;
    END