SQL Date Arithmetic

Add or subtract a number of days directly from a date using plain + and - operators — dates behave like numbers in this specific way.

What & Why

Postgres lets you add or subtract a plain integer directly to or from a DATE, and it's interpreted as a number of days. start_date + 7 means "seven days after start_date." This is the simplest form of date math — the INTERVAL lesson right after this one covers a more flexible, explicit way to express the same kind of arithmetic.

See How It Works

BUSINESS QUESTION

Marketing wants seven-day and thirty-day checkpoints derived from every campaign start date.

id	name	channel	spend	start_date	end_date	status	target_segment
1	Spring Launch	google_ads	55000.00	2024-01-15	2024-03-31	active	smb
2	Retention Webinar	email	45000.00	2024-02-10	2024-04-15	active	enterprise
3	Finance Retargeting	linkedin	50000.00	2024-03-12	2024-05-31	active	enterprise
4	Enterprise Search	google_ads	60000.00	2024-04-01	2024-06-30	active	enterprise

Watch one date move by integer day offsetsStep 1 of 3

start_date + 7

id	name	start_date	plus_7_days
1	Spring Launch	2024-01-15	2024-01-22
2	Retention Webinar	2024-02-10	2024-02-17
3	Finance Retargeting	2024-03-12	2024-03-19
4	Enterprise Search	2024-04-01	2024-04-08

Adding the integer 7 moves every displayed campaign DATE forward by exactly seven days.

EXAMPLE QUERY

SELECT
  id,
  name,
  start_date,
  start_date + 7 AS plus_7_days,
  start_date - 7 AS minus_7_days,
  start_date + 30 AS plus_30_days
FROM marketing.campaigns
ORDER BY id;

Now You Try

Practice this concept

Marketing wants seven-day and thirty-day checkpoints derived from every campaign start date.

Available schema

marketing

Prefix tables with marketing.table_name.

idnamestart_dateplus_7_daysminus_7_daysplus_30_days

marketing.campaigns

Column	Type
id	integer
name	text
channel	text
spend	numeric
start_date	date
end_date	date
status	text
target_segment	text
legacy_id	text

query.sql

Intermediate business practice