+ INTERVAL

d + INTERVAL i DAY returns the date i days after the date d.

You can also add YEAR, MONTH, DAY, HOUR, MINUTE, SECOND

You can also add a negative value.

 DATE '2006-05-20' + INTERVAL 5 DAY   -> DATE '2006-05-25' 
 DATE '2006-05-20' + INTERVAL 5 MONTH -> DATE '2006-10-20' 
 DATE '2006-05-20' + INTERVAL 5 YEAR  -> DATE '2011-05-20' 

SELECT whn, whn+INTERVAL 7 DAY
  FROM eclipse

• EXTRACT function