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Doc: clarify behavior of ALTER DEFAULT PRIVILEGES ... IN SCHEMA.

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The existing text stated that "Default privileges that are specified
per-schema are added to whatever the global default privileges are for
the particular object type".  However, that bare-bones observation is
not quite clear enough, as demonstrated by the complaint in bug #16124.
Flesh it out by stating explicitly that you can't revoke built-in
default privileges this way, and by providing an example to drive
the point home.

Back-patch to all supported branches, since it's been like this
from the beginning.

Discussion: https://postgr.es/m/16124-423d8ee4358421bc@postgresql.org
This commit is contained in:
Tom Lane 2019-11-19 14:21:41 -05:00
parent 7f338369ca
commit 787b3fd33f
1 changed files with 23 additions and 7 deletions
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30
doc/src/sgml/ref/alter_default_privileges.sgml
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@ -106,9 +106,7 @@ REVOKE [ GRANT OPTION FOR ]
You can change default privileges only for objects that will be created by
yourself or by roles that you are a member of. The privileges can be set
globally (i.e., for all objects created in the current database),
or just for objects created in specified schemas. Default privileges
that are specified per-schema are added to whatever the global default
privileges are for the particular object type.
or just for objects created in specified schemas.
</para>
<para>
@ -120,6 +118,16 @@ REVOKE [ GRANT OPTION FOR ]
<command>ALTER DEFAULT PRIVILEGES</command>.
</para>
<para>
Default privileges that are specified per-schema are added to whatever
the global default privileges are for the particular object type.
This means you cannot revoke privileges per-schema if they are granted
globally (either by default, or according to a previous <command>ALTER
DEFAULT PRIVILEGES</command> command that did not specify a schema).
Per-schema <literal>REVOKE</literal> is only useful to reverse the
effects of a previous per-schema <literal>GRANT</literal>.
</para>
<refsect2>
<title>Parameters</title>
@ -142,8 +150,8 @@ REVOKE [ GRANT OPTION FOR ]
are altered for objects later created in that schema.
If <literal>IN SCHEMA</literal> is omitted, the global default privileges
are altered.
<literal>IN SCHEMA</literal> is not allowed when using <literal>ON SCHEMAS</literal>
as schemas can't be nested.
<literal>IN SCHEMA</literal> is not allowed when setting privileges
for schemas, since schemas can't be nested.
</para>
</listitem>
</varlistentry>
@ -212,10 +220,18 @@ ALTER DEFAULT PRIVILEGES IN SCHEMA myschema REVOKE INSERT ON TABLES FROM webuser
<para>
Remove the public EXECUTE permission that is normally granted on functions,
for all functions subsequently created by role <literal>admin</literal>:
<programlisting>
ALTER DEFAULT PRIVILEGES FOR ROLE admin REVOKE EXECUTE ON FUNCTIONS FROM PUBLIC;
</programlisting></para>
</programlisting>
Note however that you <emphasis>cannot</emphasis> accomplish that effect
with a command limited to a single schema. This command has no effect,
unless it is undoing a matching <literal>GRANT</literal>:
<programlisting>
ALTER DEFAULT PRIVILEGES IN SCHEMA public REVOKE EXECUTE ON FUNCTIONS FROM PUBLIC;
</programlisting>
That's because per-schema default privileges can only add privileges to
the global setting, not remove privileges granted by it.
</para>
</refsect1>
<refsect1>