I am working on a project of a car rental at the moment. I want to create a trigger that will calculate the number of days between two dates, and display it in a new column. So I realized I need to alter my `bookings` table because I don't have a `duration` table.

    ALTER TABLE bookings
    ADD duration varchar(10);

After altering, I think I need to create an update trigger because `DATEDIFF` function is used for querying. Could someone help me with this trigger? E.g. Count the amount of days between 10th March and 15th March - 5 days. Any help is appreciated. I assume it will be an `UPDATE` trigger??