MySQL 8.0

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create table mytable (
    startdate datetime not null,
    noofdays int not null,
    enddate datetime as (startdate + interval noofdays day)
)
insert into mytable (startdate, noofdays) values(now(), 3);
select * from mytable;


startdate
noofdays
enddate


2023-07-17 10:45:58
3
2023-07-20 10:45:58