SQL Days Between Dates

The general form of the Subtract Dates lesson — computing the gap between any two arbitrary date columns, not just against today.

What & Why

Subtracting two DATE columns from each other gives the day count between them — this works identically whether one side is CURRENT_DATE or two entirely different stored columns.

See How It Works

BUSINESS QUESTION

Marketing wants each campaign duration in days.

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

EXAMPLE QUERY

SELECT
  id AS campaign_id,
  name,
  end_date - start_date AS duration_days
FROM marketing.campaigns
WHERE end_date IS NOT NULL
ORDER BY duration_days DESC, campaign_id;

RESULT — exact output from the displayed Queryflo rows

campaign_id	name	duration_days
4	Enterprise Search	90
3	Finance Retargeting	80
1	Spring Launch	76
2	Retention Webinar	65

DATE subtraction returns the real completed campaign durations.

Intermediate business practice