添加int到最新的SQL

Question

I have a table Scadenziario with many columns.

I want to add the column "Frequenza" (INT) to the column "preavviso" (DATE).

With the query

select ID, Scadenza, Frequenza
FROM scadenziario
WHERE Scadenza < '2018-12-11'

I'm going to select the row that i need

" frequenza " is an int that specify the number of day that will pass before renew the deadline (" scadenza ")

How can i add " frequenza " to " Scadenza "?

For example

ID | Scadenza  | Frequenza
1  | 2018-12-1 | 20
2  | 2018-1-1  | 40

should become

ID | Scadenza   | Frequenza
1  | 2018-12-21 | 20
2  | 2018-2-11  | 40

Answer 1

You can use DATE_ADD() function:

select ID, Scadenza, Frequenza, DATE_ADD( Scadenza, INTERVAL Frequenza DAY) 
FROM scadenziario
WHERE Scadenza < '2018-12-11'

Answer 2

I didn't understand what you exactly what to do. But if I understand correctly this is what you need to do:

ALTER TABLE `scadenziario` 
ADD COLUMN `Frequenza ` INT NULL AFTER `scadenza `;