Arithmetic with intervals

This topic describes the Firebolt implementation of arithmetic with intervals.

Overview

An interval represents a duration. In Firebolt, values of type interval can be used to add or subtract a duration to/from a date or timestamp. Interval cannot be used as the data type of a column.

The + and * operators shown below come in commutative pairs (e.g., both DATE + interval and interval + DATE are accepted).

Operator Description
DATE + interval -> TIMESTAMP Add an interval to a DATE
DATE - interval -> TIMESTAMP Subtract an interval from a DATE
TIMESTAMP + interval -> TIMESTAMP Add an interval to a TIMESTAMP
TIMESTAMP - interval -> TIMESTAMP Subtract an interval from a TIMESTAMP
TIMESTAMPTZ + interval -> TIMESTAMPTZ Add an interval to a TIMESTAMPTZ
TIMESTAMPTZ - interval -> TIMESTAMPTZ Subtract an interval from a TIMESTAMPTZ
interval * DOUBLE PRECISION -> interval Multiply an interval by a scalar

Literal string interpretation

Interval literals can be specified in two formats.

First format 

interval 'quantity unit [quantity unit...] [direction]'

where direction can be ago or empty (ago negates all the quantities), quantity is a possibly signed integer, and unit is one of the following, matched case-insensitively:

Unit
microsecond[s] / us
millisecond[s] / ms
second[s] / s
minute[s] / m
hour[s] / h
day[s] / d
week[s] / w
month[s] / mon[s]
year[s] / y
decade[s] / dec[s]
century / centuries / c
millennium[s] / mil[s]

Each unit can appear only once in an interval literal. The value of the interval is determined by adding the quantities of the specified units with the appropriate signs.

Second format 

interval 'N' unit

where N is a possibly signed integer, and unit is one of the following, matched case-insensitively:

Unit
second
minute
hour
day
week
month
year

Arithmetic between interval and TIMESTAMPTZ

Interval arithmetic with TIMESTAMPTZ values works as follows:

  1. Convert the TIMESTAMPTZ value from Unix time to local time according to the rules of the time zone specified by the session’s time_zone setting.
  2. Add the millennium, century, decade, year, month, week and day components of the interval to the local time.
  3. Convert the local time back to Unix time according to the rules of the time zone specified by the session’s time_zone setting.
  4. Add the hour, minute, second, millisecond, and microsecond components of the interval to the Unix time.

The back and forth between Unix time and local time is necessary to handle the fact that not all days consist of 24 hours due to daylight savings time transitions. For instance, SELECT TIMESTAMPTZ '2022-10-30 Europe/Berlin' + interval '1 day' returns 2022-10-31 00:00:00+01 but SELECT TIMESTAMPTZ '2022-10-30 Europe/Berlin' + interval '24 hours' returns 2022-10-30 23:00:00+01 (assuming the value of the session’s time_zone setting is 'Europe/Berlin'). Still, the dependence on the session’s time_zone setting should be kept in mind when doing arithmetic between interval and TIMESTAMPTZ.

Multiplying an interval by a scalar

You can use the expression date_time + INTERVAL * d where date_time is a constant or column reference of type DATE, TIMESTAMP, or TIMESTAMPTZ, and d is a constant or column reference of type DOUBLE PRECISION. The effect is that the INTERVAL is scaled by d, and the resulting INTERVAL is added to date_time. E.g., INTERVAL '1 day' * 3 -> INTERVAL '3 days'.

Examples 

SELECT DATE '1996-09-03' - interval '1 millennium 5 years 42 day 42 ms';  --> 0991-07-22 23:59:59.958
SELECT TIMESTAMP '1996-09-03 11:19:42' + interval '10 years 5 months 42 days 7 seconds';  --> 2007-03-17 11:19:49

SELECT TIMESTAMP '2023-10-20 11:49:52' + interval '1 year 6 months 4 weeks 7 hours' * 7.5;  --> 2035-08-20 16:19:52
SELECT DATE '2023-10-20' - 42 * interval '1 months 1 day 1 hour';  --> 2020-03-07 06:00:00

-- The following example shows a daylight savings time change in the time zone 'Europe/Berlin'
SET time_zone = 'Europe/Berlin';
SELECT TIMESTAMPTZ '2022-10-30 Europe/Berlin' + interval '1 day';  --> 2022-10-31 00:00:00+01
SELECT TIMESTAMPTZ '2022-10-30 Europe/Berlin' + interval '24' hour;  --> 2022-10-30 23:00:00+01

SET time_zone = 'US/Pacific';
SELECT TIMESTAMPTZ '2022-10-30 Europe/Berlin' + interval '1 day';  --> 2022-10-30 15:00:00-07
SELECT TIMESTAMPTZ '2022-10-30 Europe/Berlin' + interval '24' hour;  --> 2022-10-30 15:00:00-07