From: Tom Lane <tgl@sss.pgh.pa.us>
To: Dmitry Ruban <dmitry@ruban.biz>
Cc: pgsql-sql@postgresql.org
Subject: Re: unique index on fields with possible null values
Date: Thu, 26 Jul 2007 22:49:31 -0400
Message-ID: <6521.1185504571@sss.pgh.pa.us> (raw)
In-Reply-To: <248746715.20070727125938@ruban.biz>
References: <248746715.20070727125938@ruban.biz>
Dmitry Ruban <dmitry@ruban.biz> writes:
> I'm trying to find a solution for unique index on fields with possible
> null values.
You appear to be hoping that a unique index would constrain a column to
contain at most one null entry. It doesn't work like that, and I
strongly urge you to reconsider what you're using null for. I think you
are in for a world of hurt, well beyond this one particular point,
because the SQL spec's semantics for null are not designed around the
idea that it represents a single distinguishable value. What it
represents is "unknown".
regards, tom lane
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To: pgsql-sql@postgresql.org
Cc: tgl@sss.pgh.pa.us, dmitry@ruban.biz
Subject: Re: unique index on fields with possible null values
In-Reply-To: <6521.1185504571@sss.pgh.pa.us>
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