What are the best practices for handling time zones and date formats in a relational database?

1. Use Timestamps with Time Zones in Database 2. Store data in UTC Time 3.Handle Time Zone Conversions in the Application Layer

When handling time zones and date formats in a relational database, it's important to follow a few best practices. First, it's important to standardize all dates and times to a common format, such as ISO 8601, which is a standardized date and time representation. This will ensure that all data is stored in the same format and is easily readable by any application that accesses the database. Additionally, it's important to store time zone information alongside the date and time data, so that the data can be displayed correctly for users in different time zones.

Not all companies require management of multiple time zones, or MTZ as I like to call it. However, once a company is having offices and plants in different regions, this can become problematic not managing MTZ. For instance, imagine having offices in Paris, France and production facilities in Thailand. The plant manufactures a product that becomes available in stock at 5AM Thailand local time (UTC+7). This is 11PM Paris time (UTC+1). If you want to know your stock availability to date, which day do you take into account if you don't manage time zones ? This is a simple example, but it can have all sorts of impacts in the manufacturing or accounting field, on reporting notably.

Some steps I'd follow are: 1. Use ISO-8601 and time zone identifier (it can be in two fields) for future dates (like events happening in future) 2. Use UTC for present (logging) and past events Why you should do it like this is because ISO-8601 doesn't have information about location of that time zone. If for example you store Berlin, Germany (GMT+1) just as a date with +1 at the end, you don't know what location is that, and goverment can change the timezone. But that should only work for Berlin, Germany and not other timezones in +1. So you need that information as well. There are examples of this online, like Samoa losing a whole day because of the change. So that's for future events. For present and past you can always calculate.

no need to reinvent the wheel, just go with ISO format and standard SQL data type and use TIMESTAMP WITH TIME ZONE or the equivalent in the SQL dialect you are using. For T-SQL it would be datetimeoffset

Something not obvious when you start developing software: Decorrelate the storage of a date and its actual usages: display, or any kind of processing. Storing a date and its time zone needs to be done at database level with proper data types without ambiguity using ISO format. Then : - think about how you want to display the date to a user based on a number of criteria available to you. For example, information in the browser can help, or perhaps the user has some kind of location information in its profile in your application. - Manage date processing in neutral format as well (calculating delivery dates, etc.) and use tooling available to you especially in SQL language of your database if you can.

Please *do not convert* a date into a string to compare it! You'll end up with all sorts of problems. Use the native data type which provides all comparison and sorting behaviors already

I've seen many ways based on how dates were stored. Things like having number of seconds elapsed since jan 1 1970 (Unix Epoch time converter), etc. Here again, databases usually provides a good amount of functions to manage them. Your development framework might as well ! SQL Server Quick tip: If the language settings of your SSMS are in English, but the SQL Server instance is installed in French, there might be a mismatch in how the datetime values are interpreted and displayed. In this case, you will need to explicitly convert the datetime column to a datetime format... like select convert(varchar, getdate(), 21).

Consider that you may not be the first with this need, so do a bit of digging before starting the work. You might find some LinkedIn posts about it ?? Don't forget to be consistent between all elements of your technical stack. Like use Zulu format for all traces and logs of all your technical components: 2023-10-14T21:43:14.962Z

Store timestamps in UTC. This ensures consistent data regardless of the user's location. Don't store timestamps as strings or integers with offsets. Most database systems offer specific data types for storing timestamps with high precision. Separate date and time: For some use cases, it might be beneficial to have separate columns for date and time. This can simplify queries and calculations. Store time zone information: Some cases, store the user's time zone along with the UTC timestamp. This allows for easier retrieval of data. Storing future dates with time zone information can be tricky due to potential daylight saving time (DST) changes. Evaluate your needs and choose the approach that best suits your application.

Explicitly agree on date format between parties if you can. Use writing formats like UTC+1, UTC+2, etc. For technical documents, like traces and logs, you can use Zulu format, for example: 2023-10-14T21:43:14.962Z | my trace details