*** 설명 ***
date형식에 지정된 시간을 추가한다.
*** 사용예 ***
Syntax : DATE_ADD(date, INTERVAL expr type)
SELECT NOW(), DATE_ADD(NOW(),INTERVAL 1 MONTH)
=> 2016-04-12 08:51:03, 2016-05-12 08:51:03
SELECT NOW(), DATE_ADD(NOW(),INTERVAL -1 MONTH)
=> 2016-04-12 08:51:03, 2016-03-12 08:51:03
*** type 값 ***
MICROSECOND
SECOND
MINUTE
HOUR
DAY
WEEK
MONTH
QUARTER
YEAR
SECOND_MICROSECOND
MINUTE_MICROSECOND
MINUTE_SECOND
HOUR_MICROSECOND
HOUR_SECOND
HOUR_MINUTE
DAY_MICROSECOND
DAY_SECOND
DAY_MINUTE
DAY_HOUR
YEAR_MONTH
