Hi this is general how to question and does not really pertain to any particular language.
To keep it simple let's say you have a page with a list of customer's names. You click on the user to edit the user. A new page loads with text fields containing all the user's information such as first, last, email, address, etc.
Let's say I update the email address, when you click update what is the normal procedure SQL wise? Since you don't know what fields were changed do you run the UPDATE query on all fields even though not all fields may have been updated? Maybe you have an array with all fields and their values and then compare what has changed and then only update that one value? Sorry for the ignorance but I have never understood how this scenario would be handled.