Subject: Re: Add A Glossary
To: Corey Huinker <corey.huinker@gmail.com>
Cc: Roger Harkavy <rogerharkavy@gmail.com>, pgsql-hackers@postgresql.org,
 Fabien COELHO <coelho@cri.ensmp.fr>, Michael Paquier <michael@paquier.xyz>
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From: =?UTF-8?Q?J=c3=bcrgen_Purtz?= <juergen@purtz.de>
Message-ID: <0ba54895-2455-60d7-3244-36030ff2f1e4@purtz.de>
Date: Fri, 13 Mar 2020 10:18:40 +0600
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> The statement that names of schema objects are unique isn't 
> /strictly/ true, just /mostly/ true. Take the case of a unique 
> constraints. 

Concerning CONSTRAINTS you are right. Constraints seems to be an exception:

  * Their name belongs to a schema, but are not necessarily unique
    within this context:
    https://www.postgresql.org/docs/current/catalog-pg-constraint.html.
  * There is a UNIQUE index within the system catalog pg_constraints:
    "pg_constraint_conrelid_contypid_conname_index" UNIQUE, btree
    (conrelid, contypid, conname), which expresses that names are unique
    within the context of a table/constraint-type. Nevertheless tests
    have shown that some stronger restrictions exists across
    table-boarders (,which seems to be implemented in CREATE statements
    - or as a consequence of your mentioned correlation between
    constraint and index ?).

I hope that there are no more such exception to the global rule 'object 
names in a schema are unique': 
https://www.postgresql.org/docs/current/sql-createschema.html

This facts must be mentioned as a short note in glossary and in more 
detail in the later patch about the architecture.

J. Purtz


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    <blockquote type="cite"
cite="mid:CADkLM=fuijXpnjnXaaRoYNQm_P5v1ToVpC3ZeSsePdzW_DtOtg@mail.gmail.com">The
      statement that names of schema objects are unique isn't <i>strictly</i> true,
      just <i>mostly</i> true. Take the case of a unique constraints. </blockquote>
    <p>Concerning CONSTRAINTS you are right. Constraints seems to be an
      exception:</p>
    <ul>
      <li>Their name belongs to a schema, but are not necessarily unique
        within this context:
        <a class="moz-txt-link-freetext" href="https://www.postgresql.org/docs/current/catalog-pg-constraint.html">https://www.postgresql.org/docs/current/catalog-pg-constraint.html</a>.</li>
      <li>There is a UNIQUE index within the system catalog
        pg_constraints:  <tt>"pg_constraint_conrelid_contypid_conname_index"
          UNIQUE, btree (conrelid, contypid, conname)</tt>, which
        expresses that names are unique within the context of a
        table/constraint-type. Nevertheless tests have shown that some
        stronger restrictions exists across table-boarders (,which seems
        to be implemented in CREATE statements - or as a consequence of
        your mentioned correlation between constraint and index ?).<br>
      </li>
    </ul>
    <p>I hope that there are no more such exception to the global rule
      'object names in a schema are unique':
      <a class="moz-txt-link-freetext" href="https://www.postgresql.org/docs/current/sql-createschema.html">https://www.postgresql.org/docs/current/sql-createschema.html</a><br>
    </p>
    <p>This facts must be mentioned as a short note in glossary and in
      more detail in the later patch about the architecture.</p>
    <p>J. Purtz<br>
    </p>
    <p><br>
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