[sql] Add days Oracle SQL

SELECT ORDER_NUM, CUSTOMER_NUM, CUSTOMER_NAME, ADD_DAYS (ORDER_DATE, 20)
FROM CUSTOMER, ORDERS; 

Oracle Express says ADD_DAYS invalid? Any ideas what Am I doing wrong?

It's Simple.You can use

select (sysdate+2) as new_date from dual;

This will add two days from current date.

You can use the plus operator to add days to a date.

order_date + 20

In a more general way you can use "INTERVAL". Here some examples:

1) add a day

select sysdate + INTERVAL '1' DAY from dual;

2) add 20 days

select sysdate + INTERVAL '20' DAY from dual;

2) add some minutes

select sysdate + INTERVAL '15' MINUTE from dual;

If you want to add N days to your days. You can use the plus operator as follows -

SELECT ( SYSDATE + N ) FROM DUAL;

Some disadvantage of "INTERVAL '1' DAY" is that bind variables cannot be used for the number of days added. Instead, numtodsinterval can be used, like in this small example:

select trunc(sysdate) + numtodsinterval(:x, 'day') tag
from dual

See also: NUMTODSINTERVAL in Oracle Database Online Documentation