What Are Date and Time Intervals? - MySQL FAQs - Introduction to SQL Date and Time Handling

A date and time interval is special value to be used to increment or decrement a date or a time at a given date or time unit. A data and time interval should be expression in the format of "INTERVAL expression unit", where "unit" and "expression" should follow these rules:

unit                 expression value 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.MICROSECONDS' 
MINUTE_SECOND        'MINUTES:SECONDS' 
HOUR_MICROSECOND     'HOURS.MICROSECONDS' 
HOUR_SECOND          'HOURS:MINUTES:SECONDS' 
HOUR_MINUTE          'HOURS:MINUTES' 
DAY_MICROSECOND      'DAYS.MICROSECONDS' 
DAY_SECOND           'DAYS HOURS:MINUTES:SECONDS' 
DAY_MINUTE           'DAYS HOURS:MINUTES' 
DAY_HOUR             'DAYS HOURS' 
YEAR_MONTH           'YEARS-MONTHS'