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Support MERGE into updatable views.

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This allows the target relation of MERGE to be an auto-updatable or
trigger-updatable view, and includes support for WITH CHECK OPTION,
security barrier views, and security invoker views.

A trigger-updatable view must have INSTEAD OF triggers for every type
of action (INSERT, UPDATE, and DELETE) mentioned in the MERGE command.
An auto-updatable view must not have any INSTEAD OF triggers. Mixing
auto-update and trigger-update actions (i.e., having a partial set of
INSTEAD OF triggers) is not supported.

Rule-updatable views are also not supported, since there is no
rewriter support for non-SELECT rules with MERGE operations.

Dean Rasheed, reviewed by Jian He and Alvaro Herrera.

Discussion: https://postgr.es/m/CAEZATCVcB1g0nmxuEc-A+gGB0HnfcGQNGYH7gS=7rq0u0zOBXA@mail.gmail.com
This commit is contained in:
Dean Rasheed
2024-02-29 15:56:59 +00:00
parent 8b29a119fd
commit 5f2e179bd3
23 changed files with 1380 additions and 288 deletions
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42
doc/src/sgml/ref/create_view.sgml
View File

@ -192,12 +192,14 @@ CREATE VIEW [ <replaceable>schema</replaceable> . ] <replaceable>view_name</repl
<listitem>
<para>
This option controls the behavior of automatically updatable views. When
this option is specified, <command>INSERT</command> and <command>UPDATE</command>
this option is specified, <command>INSERT</command>,
<command>UPDATE</command>, and <command>MERGE</command>
commands on the view will be checked to ensure that new rows satisfy the
view-defining condition (that is, the new rows are checked to ensure that
they are visible through the view). If they are not, the update will be
rejected. If the <literal>CHECK OPTION</literal> is not specified,
<command>INSERT</command> and <command>UPDATE</command> commands on the view are
<command>INSERT</command>, <command>UPDATE</command>, and
<command>MERGE</command> commands on the view are
allowed to create rows that are not visible through the view. The
following check options are supported:
@ -247,7 +249,8 @@ CREATE VIEW [ <replaceable>schema</replaceable> . ] <replaceable>view_name</repl
<command>INSERT</command> or <command>UPDATE</command> command to be rewritten, then
all check options will be ignored in the rewritten query, including any
checks from automatically updatable views defined on top of the relation
with the <literal>INSTEAD</literal> rule.
with the <literal>INSTEAD</literal> rule. <command>MERGE</command> is not
supported if the view or any of its base relations have rules.
</para>
</listitem>
</varlistentry>
@ -360,7 +363,8 @@ CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
<para>
Simple views are automatically updatable: the system will allow
<command>INSERT</command>, <command>UPDATE</command> and <command>DELETE</command> statements
<command>INSERT</command>, <command>UPDATE</command>,
<command>DELETE</command>, and <command>MERGE</command> statements
to be used on the view in the same way as on a regular table. A view is
automatically updatable if it satisfies all of the following conditions:
@ -400,13 +404,15 @@ CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
An automatically updatable view may contain a mix of updatable and
non-updatable columns. A column is updatable if it is a simple reference
to an updatable column of the underlying base relation; otherwise the
column is read-only, and an error will be raised if an <command>INSERT</command>
or <command>UPDATE</command> statement attempts to assign a value to it.
column is read-only, and an error will be raised if an
<command>INSERT</command>, <command>UPDATE</command>, or
<command>MERGE</command> statement attempts to assign a value to it.
</para>
<para>
If the view is automatically updatable the system will convert any
<command>INSERT</command>, <command>UPDATE</command> or <command>DELETE</command> statement
<command>INSERT</command>, <command>UPDATE</command>,
<command>DELETE</command>, or <command>MERGE</command> statement
on the view into the corresponding statement on the underlying base
relation. <command>INSERT</command> statements that have an <literal>ON
CONFLICT UPDATE</literal> clause are fully supported.
@ -415,17 +421,21 @@ CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
<para>
If an automatically updatable view contains a <literal>WHERE</literal>
condition, the condition restricts which rows of the base relation are
available to be modified by <command>UPDATE</command> and <command>DELETE</command>
statements on the view. However, an <command>UPDATE</command> is allowed to
available to be modified by <command>UPDATE</command>,
<command>DELETE</command>, and <command>MERGE</command>
statements on the view. However, an <command>UPDATE</command> or
<command>MERGE</command> is allowed to
change a row so that it no longer satisfies the <literal>WHERE</literal>
condition, and thus is no longer visible through the view. Similarly,
an <command>INSERT</command> command can potentially insert base-relation rows
an <command>INSERT</command> or <command>MERGE</command> command can
potentially insert base-relation rows
that do not satisfy the <literal>WHERE</literal> condition and thus are not
visible through the view (<literal>ON CONFLICT UPDATE</literal> may
similarly affect an existing row not visible through the view).
The <literal>CHECK OPTION</literal> may be used to prevent
<command>INSERT</command> and <command>UPDATE</command> commands from creating
such rows that are not visible through the view.
<command>INSERT</command>, <command>UPDATE</command>, and
<command>MERGE</command> commands from creating such rows that are not
visible through the view.
</para>
<para>
@ -443,14 +453,16 @@ CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
<para>
A more complex view that does not satisfy all these conditions is
read-only by default: the system will not allow an insert, update, or
delete on the view. You can get the effect of an updatable view by
read-only by default: the system will not allow an <command>INSERT</command>,
<command>UPDATE</command>, <command>DELETE</command>, or <command>MERGE</command>
on the view. You can get the effect of an updatable view by
creating <literal>INSTEAD OF</literal> triggers on the view, which must
convert attempted inserts, etc. on the view into appropriate actions
on other tables. For more information see <xref
linkend="sql-createtrigger"/>. Another possibility is to create rules
(see <xref linkend="sql-createrule"/>), but in practice triggers are
easier to understand and use correctly.
easier to understand and use correctly. Also note that <command>MERGE</command>
is not supported on relations with rules.
</para>
<para>

22
doc/src/sgml/ref/merge.sgml
View File

@ -132,9 +132,9 @@ DELETE
<term><replaceable class="parameter">target_table_name</replaceable></term>
<listitem>
<para>
The name (optionally schema-qualified) of the target table to merge into.
If <literal>ONLY</literal> is specified before the table name, matching
rows are updated or deleted in the named table only. If
The name (optionally schema-qualified) of the target table or view to
merge into. If <literal>ONLY</literal> is specified before a table
name, matching rows are updated or deleted in the named table only. If
<literal>ONLY</literal> is not specified, matching rows are also updated
or deleted in any tables inheriting from the named table. Optionally,
<literal>*</literal> can be specified after the table name to explicitly
@ -142,6 +142,16 @@ DELETE
<literal>ONLY</literal> keyword and <literal>*</literal> option do not
affect insert actions, which always insert into the named table only.
</para>
<para>
If <replaceable class="parameter">target_table_name</replaceable> is a
view, it must either be automatically updatable with no
<literal>INSTEAD OF</literal> triggers, or it must have
<literal>INSTEAD OF</literal> triggers for every type of action
(<literal>INSERT</literal>, <literal>UPDATE</literal>, and
<literal>DELETE</literal>) specified in the <literal>WHEN</literal>
clauses. Views with rules are not supported.
</para>
</listitem>
</varlistentry>
@ -486,7 +496,11 @@ MERGE <replaceable class="parameter">total_count</replaceable>
the action's event type.
</para>
</listitem>
</orderedlist></para>
</orderedlist>
If the target relation is a view with <literal>INSTEAD OF ROW</literal>
triggers for the action's event type, they are used to perform the
action instead.
</para>
</listitem>
</orderedlist></para>
</listitem>

40
doc/src/sgml/rules.sgml
View File

@ -797,9 +797,9 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a;
<para>
What happens if a view is named as the target relation for an
<command>INSERT</command>, <command>UPDATE</command>, or
<command>DELETE</command>? Doing the substitutions
described above would give a query tree in which the result
<command>INSERT</command>, <command>UPDATE</command>,
<command>DELETE</command>, or <command>MERGE</command>? Doing the
substitutions described above would give a query tree in which the result
relation points at a subquery range-table entry, which will not
work. There are several ways in which <productname>PostgreSQL</productname>
can support the appearance of updating a view, however.
@ -813,11 +813,12 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a;
If the subquery selects from a single base relation and is simple
enough, the rewriter can automatically replace the subquery with the
underlying base relation so that the <command>INSERT</command>,
<command>UPDATE</command>, or <command>DELETE</command> is applied to
the base relation in the appropriate way. Views that are
<quote>simple enough</quote> for this are called <firstterm>automatically
updatable</firstterm>. For detailed information on the kinds of view that can
be automatically updated, see <xref linkend="sql-createview"/>.
<command>UPDATE</command>, <command>DELETE</command>, or
<command>MERGE</command> is applied to the base relation in the
appropriate way. Views that are <quote>simple enough</quote> for this
are called <firstterm>automatically updatable</firstterm>. For detailed
information on the kinds of view that can be automatically updated, see
<xref linkend="sql-createview"/>.
</para>
<para>
@ -827,10 +828,10 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a;
Rewriting works slightly differently
in this case. For <command>INSERT</command>, the rewriter does
nothing at all with the view, leaving it as the result relation
for the query. For <command>UPDATE</command> and
<command>DELETE</command>, it's still necessary to expand the
for the query. For <command>UPDATE</command>, <command>DELETE</command>,
and <command>MERGE</command>, it's still necessary to expand the
view query to produce the <quote>old</quote> rows that the command will
attempt to update or delete. So the view is expanded as normal,
attempt to update, delete, or merge. So the view is expanded as normal,
but another unexpanded range-table entry is added to the query
to represent the view in its capacity as the result relation.
</para>
@ -842,13 +843,13 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a;
list to identify the physical locations of the rows to be updated.
This does not work if the result relation is a view, because a view
does not have any <acronym>CTID</acronym>, since its rows do not have
actual physical locations. Instead, for an <command>UPDATE</command>
or <command>DELETE</command> operation, a special <literal>wholerow</literal>
entry is added to the target list, which expands to include all
columns from the view. The executor uses this value to supply the
<quote>old</quote> row to the <literal>INSTEAD OF</literal> trigger. It is
up to the trigger to work out what to update based on the old and
new row values.
actual physical locations. Instead, for an <command>UPDATE</command>,
<command>DELETE</command>, or <command>MERGE</command> operation, a
special <literal>wholerow</literal> entry is added to the target list,
which expands to include all columns from the view. The executor uses this
value to supply the <quote>old</quote> row to the
<literal>INSTEAD OF</literal> trigger. It is up to the trigger to work
out what to update based on the old and new row values.
</para>
<para>
@ -857,7 +858,8 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a;
<command>UPDATE</command>, and <command>DELETE</command> commands on
a view. These rules will rewrite the command, typically into a command
that updates one or more tables, rather than views. That is the topic
of <xref linkend="rules-update"/>.
of <xref linkend="rules-update"/>. Note that this will not work with
<command>MERGE</command>, which currently does not support rules.
</para>
<para>