To update a trigger in SQL, you can use the ALTER TRIGGER statement. This statement allows you to modify the trigger’s definition, including the trigger’s name, the triggering event, and the trigger’s action.

The basic syntax for updating a trigger in SQL is as follows:

ALTER TRIGGER trigger_name
ON table_name
AFTER INSERT, UPDATE, DELETE
AS
BEGIN
    -- trigger action goes here
END;

To modify the trigger definition, you simply modify the code inside the BEGIN and END statements. For example, if you wanted to change the action performed by a trigger that fires after an INSERT on a table called customers, you could use the following code:

ALTER TRIGGER my_trigger
ON customers
AFTER INSERT
AS
BEGIN
    UPDATE sales
    SET sales.total_sales = sales.total_sales + inserted.purchase_amount
    FROM sales
    JOIN inserted ON sales.customer_id = inserted.customer_id
END;

In this example, the trigger named my_trigger is modified to update the total sales for a customer in a separate sales table whenever a new purchase is inserted into the customers table. The update statement in the trigger body retrieves the customer ID and purchase amount from the inserted table (which contains the rows affected by the trigger event), and uses this information to update the corresponding row in the sales table.

Note that you need to have appropriate permissions to modify triggers in a SQL database, and that modifying a trigger can affect other database objects that rely on that trigger, such as views or stored procedures. It is generally a good practice to test any modified trigger thoroughly before deploying it to a production environment.