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doc: Improve description of RLS policies applied by command type.

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On the CREATE POLICY page, the "Policies Applied by Command Type"
table was missing MERGE ... THEN DELETE and some of the policies
applied during INSERT ... ON CONFLICT and MERGE. Fix that, and try to
improve readability by listing the various MERGE cases separately,
rather than together with INSERT/UPDATE/DELETE. Mention COPY ... TO
along with SELECT, since it behaves in the same way. In addition,
document which policy violations cause errors to be thrown, and which
just cause rows to be silently ignored.

Also, a paragraph above the table states that INSERT ... ON CONFLICT
DO UPDATE only checks the WITH CHECK expressions of INSERT policies
for rows appended to the relation by the INSERT path, which is
incorrect -- all rows proposed for insertion are checked, regardless
of whether they end up being inserted. Fix that, and also mention that
the same applies to INSERT ... ON CONFLICT DO NOTHING.

In addition, in various other places on that page, clarify how the
different types of policy are applied to different commands, and
whether or not errors are thrown when policy checks do not pass.

Backpatch to all supported versions. Prior to v17, MERGE did not
support RETURNING, and so MERGE ... THEN INSERT would never check new
rows against SELECT policies. Prior to v15, MERGE was not supported at
all.

Author: Dean Rasheed <dean.a.rasheed@gmail.com>
Reviewed-by: Viktor Holmberg <v@viktorh.net>
Reviewed-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CAEZATCWqnfeChjK=n1V_dYZT4rt4mnq+ybf9c0qXDYTVMsy8pg@mail.gmail.com
Backpatch-through: 14
This commit is contained in:
Dean Rasheed
2025-11-13 12:00:56 +00:00
parent 017249b828
commit 7dc4fa9141
1 changed files with 163 additions and 48 deletions
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211
doc/src/sgml/ref/create_policy.sgml
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@@ -49,6 +49,8 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
in <literal>WITH CHECK</literal>. When a <literal>USING</literal> in <literal>WITH CHECK</literal>. When a <literal>USING</literal>
expression returns true for a given row then that row is visible to the expression returns true for a given row then that row is visible to the
user, while if false or null is returned then the row is not visible. user, while if false or null is returned then the row is not visible.
Typically, no error occurs when a row is not visible, but see
<xref linkend="sql-createpolicy-summary"/> for exceptions.
When a <literal>WITH CHECK</literal> expression returns true for a row When a <literal>WITH CHECK</literal> expression returns true for a row
then that row is inserted or updated, while if false or null is returned then that row is inserted or updated, while if false or null is returned
then an error occurs. then an error occurs.
@@ -194,8 +196,9 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
rows for which the expression returns false or null will not be rows for which the expression returns false or null will not be
visible to the user (in a <command>SELECT</command>), and will not be visible to the user (in a <command>SELECT</command>), and will not be
available for modification (in an <command>UPDATE</command> available for modification (in an <command>UPDATE</command>
or <command>DELETE</command>). Such rows are silently suppressed; no error or <command>DELETE</command>). Typically, such rows are silently
is reported. suppressed; no error is reported (but see
<xref linkend="sql-createpolicy-summary"/> for exceptions).
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
@@ -251,8 +254,10 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
otherwise). If an <command>INSERT</command> otherwise). If an <command>INSERT</command>
or <command>UPDATE</command> command attempts to add rows to the or <command>UPDATE</command> command attempts to add rows to the
table that do not pass the <literal>ALL</literal> table that do not pass the <literal>ALL</literal>
policy's <literal>WITH CHECK</literal> expression, the entire policy's <literal>WITH CHECK</literal> expression (or its
command will be aborted. <literal>USING</literal> expression, if it does not have a
<literal>WITH CHECK</literal> expression), the entire command will
be aborted.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
@@ -268,11 +273,50 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
relation that pass the <literal>SELECT</literal> policy will be relation that pass the <literal>SELECT</literal> policy will be
returned during a <literal>SELECT</literal> query, and that queries returned during a <literal>SELECT</literal> query, and that queries
that require <literal>SELECT</literal> permissions, such as that require <literal>SELECT</literal> permissions, such as
<literal>UPDATE</literal>, will also only see those records <literal>UPDATE</literal>, <literal>DELETE</literal>, and
<literal>MERGE</literal>, will also only see those records
that are allowed by the <literal>SELECT</literal> policy. that are allowed by the <literal>SELECT</literal> policy.
A <literal>SELECT</literal> policy cannot have a <literal>WITH A <literal>SELECT</literal> policy cannot have a <literal>WITH
CHECK</literal> expression, as it only applies in cases where CHECK</literal> expression, as it only applies in cases where
records are being retrieved from the relation. records are being retrieved from the relation, except as described
below.
</para>
<para>
If a data-modifying query has a <literal>RETURNING</literal> clause,
<literal>SELECT</literal> permissions are required on the relation,
and any newly inserted or updated rows from the relation must satisfy
the relation's <literal>SELECT</literal> policies in order to be
available to the <literal>RETURNING</literal> clause. If a newly
inserted or updated row does not satisfy the relation's
<literal>SELECT</literal> policies, an error will be thrown (inserted
or updated rows to be returned are <emphasis>never</emphasis>
silently ignored).
</para>
<para>
If an <literal>INSERT</literal> has an <literal>ON CONFLICT DO
NOTHING/UPDATE</literal> clause, <literal>SELECT</literal>
permissions are required on the relation, and the rows proposed for
insertion are checked using the relation's <literal>SELECT</literal>
policies. If a row proposed for insertion does not satisfy the
relation's <literal>SELECT</literal> policies, an error is thrown
(the <literal>INSERT</literal> is <emphasis>never</emphasis> silently
avoided). In addition, if the <literal>UPDATE</literal> path is
taken, the row to be updated and the new updated row are checked
against the relation's <literal>SELECT</literal> policies, and an
error is thrown if they are not satisfied (an auxiliary
<literal>UPDATE</literal> is <emphasis>never</emphasis> silently
avoided).
</para>
<para>
A <literal>MERGE</literal> command requires <literal>SELECT</literal>
permissions on both the source and target relations, and so each
relation's <literal>SELECT</literal> policies are applied before they
are joined, and the <literal>MERGE</literal> actions will only see
those records that are allowed by those policies. In addition, if
an <literal>UPDATE</literal> action is executed, the target relation's
<literal>SELECT</literal> policies are applied to the updated row, as
for a standalone <literal>UPDATE</literal>, except that an error is
thrown if they are not satisfied.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
@@ -292,10 +336,11 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
where records are being added to the relation. where records are being added to the relation.
</para> </para>
<para> <para>
Note that <literal>INSERT</literal> with <literal>ON CONFLICT DO Note that an <literal>INSERT</literal> with an <literal>ON CONFLICT
UPDATE</literal> checks <literal>INSERT</literal> policies' DO NOTHING/UPDATE</literal> clause will check the
<literal>WITH CHECK</literal> expressions only for rows appended <literal>INSERT</literal> policies' <literal>WITH CHECK</literal>
to the relation by the <literal>INSERT</literal> path. expressions for all rows proposed for insertion, regardless of
whether or not they end up being inserted.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
@@ -305,12 +350,12 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
<listitem> <listitem>
<para> <para>
Using <literal>UPDATE</literal> for a policy means that it will apply Using <literal>UPDATE</literal> for a policy means that it will apply
to <literal>UPDATE</literal>, <literal>SELECT FOR UPDATE</literal> to <literal>UPDATE</literal>, <literal>SELECT FOR UPDATE</literal>,
and <literal>SELECT FOR SHARE</literal> commands, as well as and <literal>SELECT FOR SHARE</literal> commands, as well as
auxiliary <literal>ON CONFLICT DO UPDATE</literal> clauses of auxiliary <literal>ON CONFLICT DO UPDATE</literal> clauses of
<literal>INSERT</literal> commands. <literal>INSERT</literal> commands, and <literal>MERGE</literal>
<literal>MERGE</literal> commands containing <literal>UPDATE</literal> commands containing <literal>UPDATE</literal> actions.
actions are affected as well. Since <literal>UPDATE</literal> Since an <literal>UPDATE</literal> command
involves pulling an existing record and replacing it with a new involves pulling an existing record and replacing it with a new
modified record, <literal>UPDATE</literal> modified record, <literal>UPDATE</literal>
policies accept both a <literal>USING</literal> expression and policies accept both a <literal>USING</literal> expression and
@@ -356,7 +401,8 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
command, if the existing row does not pass the command, if the existing row does not pass the
<literal>USING</literal> expressions, an error will be thrown (the <literal>USING</literal> expressions, an error will be thrown (the
<literal>UPDATE</literal> path will <emphasis>never</emphasis> be silently <literal>UPDATE</literal> path will <emphasis>never</emphasis> be silently
avoided). avoided). The same applies to an <literal>UPDATE</literal> action
of a <command>MERGE</command> command.
</para> </para>
</listitem> </listitem>
</varlistentry> </varlistentry>
@@ -366,12 +412,18 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
<listitem> <listitem>
<para> <para>
Using <literal>DELETE</literal> for a policy means that it will apply Using <literal>DELETE</literal> for a policy means that it will apply
to <literal>DELETE</literal> commands. Only rows that pass this to <literal>DELETE</literal> commands and <literal>MERGE</literal>
policy will be seen by a <literal>DELETE</literal> command. There can commands containing <literal>DELETE</literal> actions. For a
be rows that are visible through a <literal>SELECT</literal> that are <literal>DELETE</literal> command, only rows that pass this policy
not available for deletion, if they do not pass the will be seen by the <literal>DELETE</literal> command. There can
<literal>USING</literal> expression for be rows that are visible through a <literal>SELECT</literal> policy
the <literal>DELETE</literal> policy. that are not available for deletion, if they do not pass the
<literal>USING</literal> expression for the <literal>DELETE</literal>
policy. Note, however, that a <literal>DELETE</literal> action in a
<literal>MERGE</literal> command will see rows that are visible
through <literal>SELECT</literal> policies, and if the
<literal>DELETE</literal> policy does not pass for such a row, an
error will be thrown.
</para> </para>
<para> <para>
@@ -400,6 +452,15 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
</variablelist> </variablelist>
<para>
<xref linkend="sql-createpolicy-summary"/> summarizes how the different
types of policy apply to specific commands. In the table,
<quote>check</quote> means that the policy expression is checked and an
error is thrown if it returns false or null, whereas <quote>filter</quote>
means that the row is silently ignored if the policy expression returns
false or null.
</para>
<table id="sql-createpolicy-summary"> <table id="sql-createpolicy-summary">
<title>Policies Applied by Command Type</title> <title>Policies Applied by Command Type</title>
<tgroup cols="6"> <tgroup cols="6">
@@ -424,8 +485,8 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
</thead> </thead>
<tbody> <tbody>
<row> <row>
<entry><command>SELECT</command></entry> <entry><command>SELECT</command> / <command>COPY ... TO</command></entry>
<entry>Existing row</entry> <entry>Filter existing row</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
@@ -433,64 +494,118 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
</row> </row>
<row> <row>
<entry><command>SELECT FOR UPDATE/SHARE</command></entry> <entry><command>SELECT FOR UPDATE/SHARE</command></entry>
<entry>Existing row</entry> <entry>Filter existing row</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>Existing row</entry> <entry>Filter existing row</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
</row> </row>
<row> <row>
<entry><command>INSERT</command> / <command>MERGE ... THEN INSERT</command></entry> <entry><command>INSERT</command></entry>
<entry>&mdash;</entry>
<entry>New row</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
</row>
<row>
<entry><command>INSERT ... RETURNING</command></entry>
<entry> <entry>
New row <footnote id="rls-select-priv"> Check new row&nbsp;<footnote id="rls-select-priv">
<para> <para>
If read access is required to the existing or new row (for example, If read access is required to either the existing or new row (for
a <literal>WHERE</literal> or <literal>RETURNING</literal> clause example, a <literal>WHERE</literal> or <literal>RETURNING</literal>
that refers to columns from the relation). clause that refers to columns from the relation).
</para> </para>
</footnote> </footnote>
</entry> </entry>
<entry>New row</entry> <entry>Check new row</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
</row> </row>
<row> <row>
<entry><command>UPDATE</command> / <command>MERGE ... THEN UPDATE</command></entry> <entry><command>UPDATE</command></entry>
<entry> <entry>
Existing &amp; new rows <footnoteref linkend="rls-select-priv"/> Filter existing row&nbsp;<footnoteref linkend="rls-select-priv"/> &amp;
check new row&nbsp;<footnoteref linkend="rls-select-priv"/>
</entry> </entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>Existing row</entry> <entry>Filter existing row</entry>
<entry>New row</entry> <entry>Check new row</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
</row> </row>
<row> <row>
<entry><command>DELETE</command></entry> <entry><command>DELETE</command></entry>
<entry> <entry>
Existing row <footnoteref linkend="rls-select-priv"/> Filter existing row&nbsp;<footnoteref linkend="rls-select-priv"/>
</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
<entry>Filter existing row</entry>
</row>
<row>
<entry><command>INSERT ... ON CONFLICT</command></entry>
<entry>
Check new row&nbsp;<footnote id="rls-on-conflict-priv">
<para>
Row proposed for insertion is checked regardless of whether or not a
conflict occurs.
</para>
</footnote>
</entry>
<entry>
Check new row&nbsp;<footnoteref linkend="rls-on-conflict-priv"/>
</entry> </entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>Existing row</entry>
</row> </row>
<row> <row>
<entry><command>ON CONFLICT DO UPDATE</command></entry> <entry><command>ON CONFLICT DO UPDATE</command></entry>
<entry>Existing &amp; new rows</entry> <entry>
Check existing &amp; new rows&nbsp;<footnote id="rls-on-conflict-update-priv">
<para>
New row of the auxiliary <command>UPDATE</command> command, which
might be different from the new row of the original
<command>INSERT</command> command.
</para>
</footnote>
</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
<entry>Existing row</entry> <entry>Check existing row</entry>
<entry>New row</entry> <entry>
Check new row&nbsp;<footnoteref linkend="rls-on-conflict-update-priv"/>
</entry>
<entry>&mdash;</entry> <entry>&mdash;</entry>
</row> </row>
<row>
<entry><command>MERGE</command></entry>
<entry>Filter source &amp; target rows</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
</row>
<row>
<entry><command>MERGE ... THEN INSERT</command></entry>
<entry>
Check new row&nbsp;<footnoteref linkend="rls-select-priv"/>
</entry>
<entry>Check new row</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
</row>
<row>
<entry><command>MERGE ... THEN UPDATE</command></entry>
<entry>Check new row</entry>
<entry>&mdash;</entry>
<entry>Check existing row</entry>
<entry>Check new row</entry>
<entry>&mdash;</entry>
</row>
<row>
<entry><command>MERGE ... THEN DELETE</command></entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
<entry>&mdash;</entry>
<entry>Check existing row</entry>
</row>
</tbody> </tbody>
</tgroup> </tgroup>
</table> </table>