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From: jian he <jian.universality@gmail.com>
Date: Fri, 8 Sep 2023 09:24:22 +0800
Message-ID: <CACJufxHD2kv6hCy8yjVk486+d5rcuJS2XxkNH80g9Ui6Rz81Cg@mail.gmail.com>
Subject: Re: SQL:2011 application time
To: Paul Jungwirth <pj@illuminatedcomputing.com>
Cc: Vik Fearing <vik@postgresfriends.org>, Peter Eisentraut <peter@eisentraut.org>, 
	Corey Huinker <corey.huinker@gmail.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Sat, Sep 2, 2023 at 5:58=E2=80=AFAM Paul Jungwirth
<pj@illuminatedcomputing.com> wrote:
>
>
> I don't quite understand this part:
>
>  >> Also, your implementation
>  >> requires at least one non-overlaps column, which also seems like a
>  >> confusing restriction.
>
> That's just a regular non-temporal constraint. Right? If I'm missing
> something let me know.
>

for a range primary key, is it fine to expect it to be unique, not
null and also not overlap? (i am not sure how hard to implement it).

-----------------------------------------------------------------
quote from 7IWD2-02-Foundation-2011-12.pdf. 4.18.3.2 Unique
constraints, page 97 of 1483.

4.18.3.2 Unique constraints In addition to the components of every
table constraint descriptor, a unique constraint descriptor includes:
=E2=80=94 An indication of whether it was defined with PRIMARY KEY or UNIQU=
E.
=E2=80=94 The names and positions of the unique columns specified in the
<unique column list>
 =E2=80=94 If <without overlap specification> is specified, then the name o=
f
the period specified.

If the table descriptor for base table T includes a unique constraint
descriptor indicating that the unique constraint was defined with
PRIMARY KEY, then the columns of that unique constraint constitute the
primary key of T. A table that has a primary key cannot have a proper
supertable.
A unique constraint that does not include a <without overlap
specification> on a table T is satisfied if and only if there do not
exist two rows R1 and R2 of T such that R1 and R2 have the same
non-null values in the unique columns. If a unique constraint UC on a
table T includes a <without overlap specification> WOS, then let
<application time period name> ATPN be the contained in WOS. UC is
satisfied if and only if there do not exist two rows R1 and R2 of T
such that R1 and R2 have the same non-null values in the unique
columns and the ATPN period values of R1 and R2 overlap. In addition,
if the unique constraint was defined with PRIMARY KEY, then it
requires that none of the values in the specified column or columns be
a null value.
-----------------------------------------------------------------
based on the above, the unique constraint does not specify that the
column list must be range type. UNIQUE (a, c WITHOUT OVERLAPS).
Here column "a" can be a range type (that have overlap property) and
can be not.
In fact, many of your primary key, foreign key regess test using
something like '[11,11]' (which make it more easy to understand),
which in logic is a non-range usage.
So UNIQUE (a, c WITHOUT OVERLAPS), column "a" be a non-range data type
does make sense?