Question

Question on preventing duplicated entry in my simple web form.

My table record user input from a web form, and distinguished by date e.g. DATE(). How to prevent user with the same name to enter information twice in a single date, e.g. same username cannot be entered twice in the same date, but can be entered at other date?

Answer 1

Your table should have these:

create table tablename (
...
user_id bigint, -- or whatever
date_created date,
unique key(user_id, date_created)
...
);