TIMESTAMPADD(interval, integer_exp, timestamp_exp)

Returns a timestamp offset by the specified interval.
Interval can be one of the following values

SQL_TSI_FRAC_SECOND (in billionths of a second)
SQL_TSI_SECOND
SQL_TSI_MINUTE
SQL_TSI_HOUR
SQL_TSI_DAY
SQL_TSI_WEEK
SQL_TSI_MONTH
SQL_TSI_QUARTER
SQL_TSI_YEAR

Example:

SELECT timestampadd(SQL_TSI_HOUR, 3, {ts '1998-01-11 10:00:00'})

Returns: 1998-01-11 13:00:00

Example:

SELECT timestampadd(SQL_TSI_DAY, -3, {ts '1998-01-11 10:00:00'})

Returns: 1998-01-08 10:00:00