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Date: Sat, 2 Dec 2023 10:41:01 -0800
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Subject: Re: SQL:2011 application time
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To: Peter Eisentraut <peter@eisentraut.org>,
 jian he <jian.universality@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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From: Paul Jungwirth <pj@illuminatedcomputing.com>
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On Thu, Nov 23, 2023 at 1:08 AM Peter Eisentraut <peter@eisentraut.org> wrote:
 > After further thought, I think the right solution is to change
 > btree_gist (and probably also btree_gin) to use the common RT* strategy
 > numbers.

Okay. That will mean bumping the version of btree_gist, and you must be running that version to use 
the new temporal features, or you will get silly results. Right? Is there a way to protect users 
against that and communicate they need to upgrade the extension?

This also means temporal features may not work in custom GIST opclasses. What we're saying is they 
must have an appropriate operator for RTEqualStrategyNumber (18) and RTOverlapStrategyNumber (3). 
Equal matters for the scalar key part(s), overlap for the range part. So equal is more likely to be 
an issue, but overlap matters if we want to support non-ranges (which I'd say is worth doing).

Also if they get it wrong, we won't really have any way to report an error.

I did some research on other extensions in contrib, as well as PostGIS. Here is what I found:

## btree_gin:

3 is =
18 is undefined

same for all types: macaddr8, int2, int4, int8, float4, float8, oid, timestamp, timestamptz, time, 
timetz, date, interval, inet, cidr, text, varchar, char, bytea, bit, varbit, numeric, anyenum, uuid, 
name, bool, bpchar

## cube

3 is &&
18 is <=>

## intarray

3 is &&
18 is undefined

## ltree

3 is =
18 is undefined

## hstore

3 and 18 are undefined

## seg

3 is &&
18 is undefined

## postgis: geometry

3 is &&
18 is undefined

## postgis: geometry_nd

3 is &&&
18 is undefined

I thought about looking through pgxn for more, but I haven't yet. I may still do that.
But already it seems like there is not much consistency.

So what do you think of this idea instead?:

We could add a new (optional) support function to GiST that translates "well-known" strategy numbers 
into the opclass's own strategy numbers. This would be support function 12. Then we can say 
translateStrategyNumber(RTEqualStrategyNumber) and look up the operator with the result.

There is not a performance hit, because we do this for the DDL command (create pk/uq/fk), then store 
the operator in the index/constraint.

If you don't provide this new support function, then creating the pk/uq/fk fails with a hint about 
what you can do to make it work.

This approach means we don't change the rules about GiST opclasses: you can still use the stranums 
how you like.

This function would also let me support non-range "temporal" foreign keys, where I'll need to build 
queries with && and maybe other operators.

What do you think?

-- 
Paul              ~{:-)
pj@illuminatedcomputing.com