MySQL query with specific timezone

Question

I have a database storing data for my Laravel/PHP application. All data is stored in the database as UTC.

I'm writing a query to get data grouped by date and hour so I can plot the data on a graph.

Our UI shows reporting data in the America/Los_Angeles timezone.

What I'm looking to do is get the last three days data but queried based on the reporting timezone of America/Los_Angeles .

To get the BETWEEN dates I'm using the below

$from = now()
    ->startOfDay()
    ->subDays(3)
    ->timezone('America/Los_Angeles');

$to = now()
    ->endOfDay()
    ->timezone('America/Los_Angeles');

This works OK. So the next step is grouping the data but not grouping it on the column data as that would be UTC . I would like to group is on the Los_Angeles timezone. So I'm doing the below.

SELECT
  DATE(CONVERT_TZ(created_at, '+00:00', '-07:00')) AS grouped_date,
  HOUR(CONVERT_TZ(created_at, '+00:00', '-07:00')) AS grouped_hour,
  count(*) AS requests
FROM
  `advert_requests`
WHERE
  created_at BETWEEN '2022-09-09 17:00:00' AND '2022-09-13 16:59:59'
GROUP BY
  grouped_date,
  grouped_hour

The random issue I'm having is that the grouped data is starting on 2022-09-09 at 10:00 and I'm not sure why.

Starting the BETWEEN at 2022-09-09 17:00:00 America/Los_Angeles is 2022-09-10 00:00:00 UTC so when doing the CONVERT_TZ on the created_at shouldn't the grouped data start at 0 ?

Any ideas?

Answer 1

Surely this isn't as easy as just setting the timezone to the reporting timezone for the sessions where I run the reporting SELECT query.

So I can leave everything else as UTC . My application is UTC and handles timezone conversion in the php/application. My database is set to UTC . My MySQL INSERT 's etc are all UTC . Then when I want to query anything to be displayed in our UI using our fixed reporting timezone of America/Los_Angeles I can just set it before running the SELECT query?

SET time_zone = '-07:00';

// In the Laravel framework
// DB::update('SET time_zone = ?', ['-07:00']);

And then

SELECT
  DATE(created_at) AS grouped_date,
  HOUR(created_at) AS grouped_hour,
  count(*) AS requests
FROM
  `advert_requests`
WHERE
  created_at BETWEEN '2022-09-10 00:00:00'
  AND '2022-09-13 23:59:59'
GROUP BY
  grouped_date,
  grouped_hour