Date: Fri, 27 Sep 2019 12:37:47 -0400
From: Bruce Momjian <bruce@momjian.us>
To: tuomas.leikola@gmail.com, pgsql-docs@lists.postgresql.org
Subject: Re: uniqueness and null could benefit from a hint for dba
Message-ID: <20190927163747.GE31412@momjian.us>
References: <156760275564.1127.12321702656456074572@wrigleys.postgresql.org>
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On Wed, Sep  4, 2019 at 01:12:35PM +0000, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/11/indexes-unique.html
> Description:
> 
> Sometimes it is convenient to create an unique index that considers NULL
> values equal. Designating a "zero" value for those rows might not be
> feasible, for example due to a foreign key.
> 
> The documentation currently only states that unique indexes do not consider
> NULLs equal. It might be good to offer workarounds, like indexing a coalesce
> function, if scans are not the reason for the index, but the uniqueness
> constraint.

I did write a blog entry about this:

	https://momjian.us/main/blogs/pgblog/2017.html#April_3_2017

Does that help?

-- 
  Bruce Momjian  <bruce@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 +