How to add one/two/n days or hours to date in MySQL (DATE_ADD in MYSQL)

Suppose you have a table in the database where the stored data and you need to check or get that dates but with the changes – calculate directly by MySQL.
Example, you want to get users end dates (7-day licence after registration):

SELECT `register_date`, `uid`, 
DATE_ADD(`register_date`, INTERVAL 7 DAY) AS `end_date` 
FROM `...`
WHERE...

Perfect, now you can show for user that his licence if over `end_date`…
In addition, you can subtract the required number of days

Just add minus before interval number.
Example, you want to get active 7-day licence users:

SELECT `register_date`, `uid`
FROM `...`
WHERE `register_date` > DATE_ADD(NOW(), INTERVAL -7 DAY) 

Also, if you meet ADDDATE() don’t afraid, is a synonym for DATE_ADD()

MySQL support:
The following table shows the expected form of the expr argument for each unit value.

unit Value

Expected expr Format
MICROSECOND MICROSECONDS
SECOND SECONDS
MINUTE MINUTES
HOUR HOURS
DAY DAYS
WEEK WEEKS
MONTH MONTHS
QUARTER QUARTERS
YEAR YEARS
SECOND_MICROSECOND ‘SECONDS.MICROSECONDS’
MINUTE_MICROSECOND ‘MINUTES:SECONDS.MICROSECONDS’
MINUTE_SECOND ‘MINUTES:SECONDS’
HOUR_MICROSECOND ‘HOURS:MINUTES:SECONDS.MICROSECONDS’
HOUR_SECOND ‘HOURS:MINUTES:SECONDS’
HOUR_MINUTE ‘HOURS:MINUTES’
DAY_MICROSECOND ‘DAYS HOURS:MINUTES:SECONDS.MICROSECONDS’
DAY_SECOND ‘DAYS HOURS:MINUTES:SECONDS’
DAY_MINUTE ‘DAYS HOURS:MINUTES’
DAY_HOUR ‘DAYS HOURS’
YEAR_MONTH ‘YEARS-MONTHS’

http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html