Re: collation, arrays, and ranges

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: collation, arrays, and ranges
Date: 2011-09-10 17:21:19
Message-ID: 18979.1315675279@sss.pgh.pa.us
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Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> My interpretation of collation for range types is different than that
> for arrays, so I'm presenting it here in case someone has an objection.

> An array type has the same typcollation as its element type. This makes
> sense, because comparison between arrays are affected by the COLLATE
> clause.

> Comparison between ranges should not be affected by the COLLATE clause
> (as we discussed).

Check.

> So, I chose to represent that as a separate
> rngcollation and leave the typcollation 0. In other words, collation is
> a concept internal to that range type and fixed at type definition time.
> Range types are affected by their internal collation, but don't take
> part in the logic that passes collation through the type system.

Should I read that as saying you want to add yet another column to
pg_type? I'd prefer not to do that. Seems to me we could still store
the value in typcollation, but just interpret the column a bit
differently depending on typtype.

regards, tom lane

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