Adding Days or Hours or Minutes or Seconds into date in MySQL (AddDate)

// The given query add a interval of 31 days to the '2012-04-15'.
ADDDATE('2012-04-15 16:30:30', INTERVAL 2 DAY); // Output: 2012-04-17 16:30:30
ADDDATE('2012-04-15 16:30:30', INTERVAL 3 HOUR); // Output: 2012-04-17 19:30:30
ADDDATE('2012-04-15 16:30:30', INTERVAL 45 MINUTE); // Output: 2012-04-17 17:15:30
ADDDATE('2012-04-15 16:30:30', INTERVAL 15 SECOND) // Output: 2012-04-17 16:30:45

//Sample MySQL Query
SELECT ADDDATE(date_user_created, INTERVAL 3 HOUR) as length_of_quote FROM users where user_id='23'

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