Date and Time calculations using INTERVAL - with examples in PostgreSQL.

Saying time is important is to state the obvious. Our lives are built on time. We only have so much of it and once it is gone, there is no getting it back. While not as important as that time, date and time data values are integral pieces in most –if not all– database infrastructure and design. At some point or another, date and time values must be considered. PostgreSQL has many functions and options for date and time value manipulation. In this post, I look at the INTERVAL type for date and time calculations….

bedside-clock — Photo by petradr on Unsplash

Note: All data, names or naming found within the database presented in this post, are strictly used for practice, learning, instruction, and testing purposes. It by no means depicts actual data belonging to or being used by any party or organization.

OS and DB used:

Xubuntu Linux 18.04.2 LTS (Bionic Beaver)
PostgreSQL 11.2

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I’ll use a couple of tables from the PostgreSQL practice DVD Rental database for the example queries below.

Let’s visit the arbitrary query below for customers whose first names begin with ‘Z’, limiting the results to just 10 for better on-screen readability:

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Suppose you need to know when 7 days have elapsed for a rented DVD. You can use INTERVAL and perform the date arithmetic:

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Be mindful of the surrounding quotes for the INTERVAL value, for without them, you get an error:

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SELECT
c.first_name AS first_name,
c.last_name AS last_name,
r.rental_date AS rent_day,
r.rental_date + INTERVAL 7 DAY AS late_return_day
FROM customer AS c
INNER JOIN rental AS r
ON c.customer_id = r.customer_id
WHERE c.first_name LIKE 'Z%'
LIMIT 10;
ERROR: syntax error at or near "7"
LINE 5: r.rental_date + INTERVAL 7 DAY AS late_return_day

INTERVAL calculations can use hour time values as well.

Imagine the same DVD rental store has a ’12 Hours of Madness’ special where you can get any number of DVD’s you want to rent for $1/each, but they must be returned within 12 hours.

Use INTERVAL in the query to determine when the 12 hour time period is up:

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Although this blog post touches on just a couple of simple example date and time calculations, check out INTERVAL for yourself to test all it has to offer..

Like what you have read? See anything incorrect? Please comment below and thanks for reading!!!

Explore the official PostgreSQL 11 On-line Documentation for more information.

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Josh Otwell has a passion to study and grow as a SQL Developer and blogger. Other favorite activities find him with his nose buried in a good book, article, or the Linux command line. Among those, he shares a love of tabletop RPG games, reading fantasy novels, and spending time with his wife and two daughters.

Disclaimer: The examples presented in this post are hypothetical ideas of how to achieve similar types of results. They are not the utmost best solution(s). The majority, if not all, of the examples provided, is performed on a personal development/learning workstation-environment and should not be considered production quality or ready. Your particular goals and needs may vary. Use those practices that best benefit your needs and goals. Opinions are my own.

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Date and Time calculations using INTERVAL – with examples in PostgreSQL.

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