Mention that the table is not modified if it already exists.
Reported-by: frank_limpert@yahoo.com
Discussion: https://postgr.es/m/
164441177106.9677.
5991676148704507229@wrigleys.postgresql.org
Backpatch-through: 10
<term><literal>IF NOT EXISTS</literal></term>
<listitem>
<para>
- Do not throw an error if a relation with the same name already exists.
- A notice is issued in this case. Refer to <xref linkend="sql-createtable"/>
- for details.
+ Do not throw an error if a relation with the same name already
+ exists; simply issue a notice and leave the table unmodified.
</para>
</listitem>
</varlistentry>