Re: Content for talk on Postgres Type System at PostgresConf

On 29 Feb 2024, at 14:51, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>>> - time with time zone *does* store the time zone, but this isn’t
>>> actually useful and should be avoided (I’m not entirely sure why and the
>>> docs only gesture at the problems without stating them, IIRC)
>
>> No it doesn't store the time zone. Nor do the docs say they do. And
>> clearly point out the issue that evaluating a time zone without both date
>> and time inputs is basically pointless.
>
> timetz *does* store a time zone, in the sense of storing a numeric
> offset from UTC (i.e., "so many minutes east or west of Greenwich").
> The problem is that in most real-world applications your notion of
> "time zone" probably includes annual DST changes, which timetz can't
> represent. I don't say the type is completely useless, but its
> usefulness is a lot less than you might guess.

The closest I can come to this in the docs is:

"The appropriate time zone offset is recorded in the time with time zone value and is output as stored; it is not adjusted to the active time zone.”

I expect to be submitting some documentation updates as part of this project, fwiw.