On Sat, Sep 1, 2018 at 07:30:43PM -0400, Tom Lane wrote: > Bruce Momjian <br...@momjian.us> writes: > > Looking over the AT TIME ZONE docs, I think they are subtly confusing. > > The order of conversion specific in the first example should _start_ > > with the assumption of local time zone for the time stamp, not something > > that happens after AT TIME ZONE is applied. The ordering in current > > docs makes the second example confusing too. > > > The attached patch fixes this. > > I think it's you that are confused. The text as written is correct, > or at least arguably so; your revision is definitely incorrect. > > SELECT TIMESTAMP '2001-02-16 20:38:40' AT TIME ZONE 'MST'; > > The way I'd describe this is that we start with a timestamp, > which has no particular timezone. The AT TIME ZONE says "Assume that > this zoneless timestamp is in MST, and convert it to timestamp with > time zone (which will be in UTC, internally)". Then after that, the > UTC timestamptz value is converted to PST8PDT for display purposes, > but that's done by timestamptz_out not AT TIME ZONE. > > If we were going from PST to MST as your patch describes it, the > output would be one hour later not one hour earlier than the input. > > SELECT TIMESTAMP WITH TIME ZONE '2001-02-16 20:38:40-05' AT TIME ZONE 'MST'; > > Here we've got a time value that was initially given in EST (-05), > but was converted to UTC by timestampz_in. Then the AT TIME ZONE > says "Please convert this UTC value to MST, and emit it as a zoneless > timestamp" (which will not be subject to any further conversion when > it's displayed). > > The existing text is indeed a bit deficient, because it fails to > draw a clear boundary between what the AT TIME ZONE operator is > doing and what is being done by the timestamp(tz) I/O functions. > But you're not making it better.
Yes, I am still researching and realize my diff is wrong. Let me keep working and I will repost. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription +
