Скачать или смотреть Converting timestamp without timezone to Local Hour in PostgreSQL

Learn how to effectively convert a `timestamp without timezone` and an integer timezone to a new timestamp in PostgreSQL, allowing accurate hour extraction.
---
This video is based on the question https://stackoverflow.com/q/70866836/ asked by the user 'Matías L.' ( https://stackoverflow.com/u/17906137/ ) and on the answer https://stackoverflow.com/a/70867148/ provided by the user 'Matías L.' ( https://stackoverflow.com/u/17906137/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to convert timestamp without timezone and integer representing timezone to a new timestamp without timezone in PostgreSQL

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Mastering Timestamp Conversion in PostgreSQL

Working with timestamps in PostgreSQL can sometimes be tricky, especially when dealing with timezones. If you've ever faced a situation where you need to adjust a timestamp without timezone using an integer representing a timezone, you know that getting the correct local hour isn't always straightforward. In this guide, we will explore how to properly convert a timestamp and timezone into a new adjusted timestamp for accurate hour extraction.

The Challenge

Imagine a table with the following structure:

snapshot_datetimezone2021-01-12 08:00:00-32021-01-12 00:00:00-5In this table:

snapshot_date represents a timestamp without an associated timezone.

timezone is an integer that represents the offset from UTC.

Your goal is to extract the correct local hour after adjusting the snapshot date by the given timezone. The challenge arises because directly performing arithmetic operations on the timestamp and integer can lead to unexpected results. For instance, adding -5 to 0 can yield -5, but after adjusting for UTC, the correct hour for your second row should actually be 19. So how do we achieve that?

The Solution

To effectively adjust the snapshot_date based on the timezone, we can use PostgreSQL's interval functionality. Here’s how to perform the adjustment step-by-step:

Step 1: Understand Interval Arithmetic

PostgreSQL allows you to perform arithmetic by treating the timezone as an interval. Instead of simply adding or subtracting from the hour, you can represent the timezone shift using an interval expression.

Step 2: Write the Conversion Query

The query you can use involves adding a calculated interval to your snapshot_date. Here is the SQL code that achieves this:

[[See Video to Reveal this Text or Code Snippet]]

This command effectively adjusts the snapshot_date by the timezone specified, ensuring you're working with the correct local time.

Step 3: Verify Results

You can test this query against your original table. For the rows given above, the results would yield:

For 2021-01-12 08:00:00 with timezone -3, the adjusted hour becomes 5.

For 2021-01-12 00:00:00 with timezone -5, after adjustment, the hour correctly becomes 19.

Conclusion

By applying the adjustment to the timestamp using the interval in PostgreSQL, you can ensure that your extracted hour aligns with the local timezone. This approach not only handles possible negative offsets but also ensures clarity in your datetime manipulations.

Mastering timestamp conversion can significantly improve your data analysis processes, so the next time you need to take timezones into account, remember this handy method. Happy querying!