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Commita99c42f

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Support automatically-updatable views.
This patch makes "simple" views automatically updatable, without the needto create either INSTEAD OF triggers or INSTEAD rules. "Simple" viewsare those classified as updatable according to SQL-92 rules. The rewritertransforms INSERT/UPDATE/DELETE commands on such views directly into anequivalent command on the underlying table, which will generally havenoticeably better performance than is possible with either triggers oruser-written rules. A view that has INSTEAD OF triggers or INSTEAD rulescontinues to operate the same as before.For the moment, security_barrier views are not considered simple.Also, we do not support WITH CHECK OPTION. These features may beadded in future.Dean Rasheed, reviewed by Amit Kapila
1 parentd12d9f5 commita99c42f

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20 files changed

+2491
-93
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20 files changed

+2491
-93
lines changed

‎doc/src/sgml/intro.sgml

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -110,7 +110,7 @@
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<simpara>triggers</simpara>
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</listitem>
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<listitem>
113-
<simpara>views</simpara>
113+
<simpara>updatableviews</simpara>
114114
</listitem>
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<listitem>
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<simpara>transactional integrity</simpara>

‎doc/src/sgml/ref/alter_table.sgml

Lines changed: 3 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -147,11 +147,9 @@ ALTER TABLE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable>
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<listitem>
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<para>
149149
These forms set or remove the default value for a column.
150-
The default values only apply to subsequent <command>INSERT</command>
151-
commands; they do not cause rows already in the table to change.
152-
Defaults can also be created for views, in which case they are
153-
inserted into <command>INSERT</> statements on the view before
154-
the view's <literal>ON INSERT</literal> rule is applied.
150+
Default values only apply in subsequent <command>INSERT</command>
151+
or <command>UPDATE</> commands; they do not cause rows already in the
152+
table to change.
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</para>
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</listitem>
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</varlistentry>

‎doc/src/sgml/ref/alter_view.sgml

Lines changed: 5 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -80,10 +80,11 @@ ALTER VIEW [ IF EXISTS ] <replaceable class="parameter">name</replaceable> RESET
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<listitem>
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<para>
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These forms set or remove the default value for a column.
83-
A default value associated with a view column is
84-
inserted into <command>INSERT</> statements on the view before
85-
the view's <literal>ON INSERT</literal> rule is applied, if
86-
the <command>INSERT</> does not specify a value for the column.
83+
A view column's default value is substituted into any
84+
<command>INSERT</> or <command>UPDATE</> command whose target is the
85+
view, before applying any rules or triggers for the view. The view's
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default will therefore take precedence over any default values from
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underlying relations.
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</para>
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</listitem>
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</varlistentry>

‎doc/src/sgml/ref/create_rule.sgml

Lines changed: 19 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -45,10 +45,10 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
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additional commands to be executed when a given command on a given
4646
table is executed. Alternatively, an <literal>INSTEAD</literal>
4747
rule can replace a given command by another, or cause a command
48-
not to be executed at all. Rules are used to implementtable
48+
not to be executed at all. Rules are used to implementSQL
4949
views as well. It is important to realize that a rule is really
5050
a command transformation mechanism, or command macro. The
51-
transformation happens before the execution of thecommands starts.
51+
transformation happens before the execution of thecommand starts.
5252
If you actually want an operation that fires independently for each
5353
physical row, you probably want to use a trigger, not a rule.
5454
More information about the rules system is in <xref linkend="rules">.
@@ -73,13 +73,11 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
7373
sufficient for your purposes) to replace update actions on the view
7474
with appropriate updates on other tables. If you want to support
7575
<command>INSERT RETURNING</> and so on, then be sure to put a suitable
76-
<literal>RETURNING</> clause into each of these rules. Alternatively,
77-
an updatable view can be implemented using <literal>INSTEAD OF</>
78-
triggers (see <xref linkend="sql-createtrigger">).
76+
<literal>RETURNING</> clause into each of these rules.
7977
</para>
8078

8179
<para>
82-
There is a catch if you try to use conditional rules for view
80+
There is a catch if you try to use conditional rules forcomplexview
8381
updates: there <emphasis>must</> be an unconditional
8482
<literal>INSTEAD</literal> rule for each action you wish to allow
8583
on the view. If the rule is conditional, or is not
@@ -95,6 +93,21 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
9593
<literal>INSTEAD NOTHING</literal> action. (This method does not
9694
currently work to support <literal>RETURNING</> queries, however.)
9795
</para>
96+
97+
<note>
98+
<para>
99+
A view that is simple enough to be automatically updatable (see <xref
100+
linkend="sql-createview">) does not require a user-created rule in
101+
order to be updatable. While you can create an explicit rule anyway,
102+
the automatic update transformation will generally outperform an
103+
explicit rule.
104+
</para>
105+
106+
<para>
107+
Another alternative worth considering is to use <literal>INSTEAD OF</>
108+
triggers (see <xref linkend="sql-createtrigger">) in place of rules.
109+
</para>
110+
</note>
98111
</refsect1>
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100113
<refsect1>

‎doc/src/sgml/ref/create_view.sgml

Lines changed: 109 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -127,17 +127,6 @@ CREATE [ OR REPLACE ] [ TEMP | TEMPORARY ] VIEW <replaceable class="PARAMETER">n
127127
<refsect1>
128128
<title>Notes</title>
129129

130-
<para>
131-
Currently, views are read only: the system will not allow an insert,
132-
update, or delete on a view. You can get the effect of an updatable
133-
view by creating <literal>INSTEAD</> triggers on the view, which
134-
must convert attempted inserts, etc. on the view into
135-
appropriate actions on other tables. For more information see
136-
<xref linkend="sql-createtrigger">. Another possibility is to create
137-
rules (see <xref linkend="sql-createrule">), but in practice triggers
138-
are easier to understand and use correctly.
139-
</para>
140-
141130
<para>
142131
Use the <xref linkend="sql-dropview">
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statement to drop views.
@@ -175,6 +164,105 @@ CREATE VIEW vista AS SELECT text 'Hello World' AS hello;
175164
to replace it (this includes being a member of the owning role).
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</para>
177166

167+
<refsect2 id="SQL-CREATEVIEW-updatable-views">
168+
<title id="SQL-CREATEVIEW-updatable-views-title">Updatable Views</title>
169+
170+
<indexterm zone="sql-createview-updatable-views">
171+
<primary>updatable views</primary>
172+
</indexterm>
173+
174+
<para>
175+
Simple views are automatically updatable: the system will allow
176+
<command>INSERT</>, <command>UPDATE</> and <command>DELETE</> statements
177+
to be used on the view in the same way as on a regular table. A view is
178+
automatically updatable if it satisfies all of the following conditions:
179+
180+
<itemizedlist>
181+
<listitem>
182+
<para>
183+
The view must have exactly one entry in its <literal>FROM</> list,
184+
which must be a table or another updatable view.
185+
</para>
186+
</listitem>
187+
188+
<listitem>
189+
<para>
190+
The view definition must not contain <literal>WITH</>,
191+
<literal>DISTINCT</>, <literal>GROUP BY</>, <literal>HAVING</>,
192+
<literal>LIMIT</>, or <literal>OFFSET</> clauses at the top level.
193+
</para>
194+
</listitem>
195+
196+
<listitem>
197+
<para>
198+
The view definition must not contain set operations (<literal>UNION</>,
199+
<literal>INTERSECT</> or <literal>EXCEPT</>) at the top level.
200+
</para>
201+
</listitem>
202+
203+
<listitem>
204+
<para>
205+
All columns in the view's select list must be simple references to
206+
columns of the underlying relation. They cannot be expressions,
207+
literals or functions. System columns cannot be referenced, either.
208+
</para>
209+
</listitem>
210+
211+
<listitem>
212+
<para>
213+
No column of the underlying relation can appear more than once in
214+
the view's select list.
215+
</para>
216+
</listitem>
217+
218+
<listitem>
219+
<para>
220+
The view must not have the <literal>security_barrier</> property.
221+
</para>
222+
</listitem>
223+
</itemizedlist>
224+
</para>
225+
226+
<para>
227+
If the view is automatically updatable the system will convert any
228+
<command>INSERT</>, <command>UPDATE</> or <command>DELETE</> statement
229+
on the view into the corresponding statement on the underlying base
230+
relation.
231+
</para>
232+
233+
<para>
234+
If an automatically updatable view contains a <literal>WHERE</>
235+
condition, the condition restricts which rows of the base relation are
236+
available to be modified by <command>UPDATE</> and <command>DELETE</>
237+
statements on the view. However, an <command>UPDATE</> is allowed to
238+
change a row so that it no longer satisfies the <literal>WHERE</>
239+
condition, and thus is no longer visible through the view. Similarly,
240+
an <command>INSERT</> command can potentially insert base-relation rows
241+
that do not satisfy the <literal>WHERE</> condition and thus are not
242+
visible through the view.
243+
</para>
244+
245+
<para>
246+
A more complex view that does not satisfy all these conditions is
247+
read-only by default: the system will not allow an insert, update, or
248+
delete on the view. You can get the effect of an updatable view by
249+
creating <literal>INSTEAD OF</> triggers on the view, which must
250+
convert attempted inserts, etc. on the view into appropriate actions
251+
on other tables. For more information see <xref
252+
linkend="sql-createtrigger">. Another possibility is to create rules
253+
(see <xref linkend="sql-createrule">), but in practice triggers are
254+
easier to understand and use correctly.
255+
</para>
256+
257+
<para>
258+
Note that the user performing the insert, update or delete on the view
259+
must have the corresponding insert, update or delete privilege on the
260+
view. In addition the view's owner must have the relevant privileges on
261+
the underlying base relations, but the user performing the update does
262+
not need any permissions on the underlying base relations (see
263+
<xref linkend="rules-privileges">).
264+
</para>
265+
</refsect2>
178266
</refsect1>
179267

180268
<refsect1>
@@ -217,11 +305,15 @@ CREATE VIEW <replaceable class="parameter">name</replaceable> [ ( <replaceable c
217305
<term><literal>CHECK OPTION</literal></term>
218306
<listitem>
219307
<para>
220-
This option has to do with updatable views. All
221-
<command>INSERT</> and <command>UPDATE</> commands on the view
222-
will be checked to ensure data satisfy the view-defining
223-
condition (that is, the new data would be visible through the
224-
view). If they do not, the update will be rejected.
308+
This option controls the behavior of automatically updatable views.
309+
When given, <command>INSERT</> and <command>UPDATE</> commands on
310+
the view will be checked to ensure new rows satisfy the
311+
view-defining condition (that is, the new rows would be visible
312+
through the view). If they do not, the update will be rejected.
313+
Without <literal>CHECK OPTION</literal>, <command>INSERT</> and
314+
<command>UPDATE</> commands on the view are allowed to create rows
315+
that are not visible through the view. (The latter behavior is the
316+
only one currently provided by <productname>PostgreSQL</>.)
225317
</para>
226318
</listitem>
227319
</varlistentry>
@@ -252,6 +344,7 @@ CREATE VIEW <replaceable class="parameter">name</replaceable> [ ( <replaceable c
252344
<command>CREATE OR REPLACE VIEW</command> is a
253345
<productname>PostgreSQL</productname> language extension.
254346
So is the concept of a temporary view.
347+
The <literal>WITH</> clause is an extension as well.
255348
</para>
256349
</refsect1>
257350

‎doc/src/sgml/rules.sgml

Lines changed: 38 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -808,13 +808,28 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a;
808808
<para>
809809
What happens if a view is named as the target relation for an
810810
<command>INSERT</command>, <command>UPDATE</command>, or
811-
<command>DELETE</command>?Simply doing the substitutions
811+
<command>DELETE</command>?Doing the substitutions
812812
described above would give a query tree in which the result
813813
relation points at a subquery range-table entry, which will not
814-
work. Instead, the rewriter assumes that the operation will be
815-
handled by an <literal>INSTEAD OF</> trigger on the view.
816-
(If there is no such trigger, the executor will throw an error
817-
when execution starts.) Rewriting works slightly differently
814+
work. There are several ways in which <productname>PostgreSQL</>
815+
can support the appearance of updating a view, however.
816+
</para>
817+
818+
<para>
819+
If the subquery selects from a single base relation and is simple
820+
enough, the rewriter can automatically replace the subquery with the
821+
underlying base relation so that the <command>INSERT</command>,
822+
<command>UPDATE</command>, or <command>DELETE</command> is applied to
823+
the base relation in the appropriate way. Views that are
824+
<quote>simple enough</> for this are called <firstterm>automatically
825+
updatable</>. For detailed information on the kinds of view that can
826+
be automatically updated, see <xref linkend="sql-createview">.
827+
</para>
828+
829+
<para>
830+
Alternatively, the operation may be handled by a user-provided
831+
<literal>INSTEAD OF</> trigger on the view.
832+
Rewriting works slightly differently
818833
in this case. For <command>INSERT</command>, the rewriter does
819834
nothing at all with the view, leaving it as the result relation
820835
for the query. For <command>UPDATE</command> and
@@ -842,10 +857,8 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a;
842857
</para>
843858

844859
<para>
845-
If there are no <literal>INSTEAD OF</> triggers to update the view,
846-
the executor will throw an error, because it cannot automatically
847-
update a view by itself. To change this, we can define rules that
848-
modify the behavior of <command>INSERT</command>,
860+
Another possibility is for the user to define <literal>INSTEAD</>
861+
rules that specify substitute actions for <command>INSERT</command>,
849862
<command>UPDATE</command>, and <command>DELETE</command> commands on
850863
a view. These rules will rewrite the command, typically into a command
851864
that updates one or more tables, rather than views. That is the topic
@@ -860,6 +873,22 @@ SELECT t1.a, t2.b, t1.ctid FROM t1, t2 WHERE t1.a = t2.a;
860873
evaluated first, and depending on the result, the triggers may not be
861874
used at all.
862875
</para>
876+
877+
<para>
878+
Automatic rewriting of an <command>INSERT</command>,
879+
<command>UPDATE</command>, or <command>DELETE</command> query on a
880+
simple view is always tried last. Therefore, if a view has rules or
881+
triggers, they will override the default behavior of automatically
882+
updatable views.
883+
</para>
884+
885+
<para>
886+
If there are no <literal>INSTEAD</> rules or <literal>INSTEAD OF</>
887+
triggers for the view, and the rewriter cannot automatically rewrite
888+
the query as an update on the underlying base relation, an error will
889+
be thrown because the executor cannot update a view as such.
890+
</para>
891+
863892
</sect2>
864893

865894
</sect1>

‎src/backend/catalog/information_schema.sql

Lines changed: 6 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -730,10 +730,8 @@ CREATE VIEW columns AS
730730
CAST('NEVER'AS character_data)AS is_generated,
731731
CAST(nullAS character_data)AS generation_expression,
732732

733-
CAST(CASE WHENc.relkind='r'
734-
OR (c.relkind='v'
735-
AND EXISTS (SELECT1FROM pg_rewriteWHERE ev_class=c.oidAND ev_type='2'AND is_instead)
736-
AND EXISTS (SELECT1FROM pg_rewriteWHERE ev_class=c.oidAND ev_type='4'AND is_instead))
733+
CAST(CASE WHENc.relkind='r'OR
734+
(c.relkind='v'AND pg_view_is_updatable(c.oid))
737735
THEN'YES' ELSE'NO' ENDAS yes_or_no)AS is_updatable
738736

739737
FROM (pg_attribute aLEFT JOIN pg_attrdef adON attrelid= adrelidAND attnum= adnum)
@@ -1896,9 +1894,8 @@ CREATE VIEW tables AS
18961894
CAST(nt.nspnameAS sql_identifier)AS user_defined_type_schema,
18971895
CAST(t.typnameAS sql_identifier)AS user_defined_type_name,
18981896

1899-
CAST(CASE WHENc.relkind='r'
1900-
OR (c.relkind='v'
1901-
AND EXISTS (SELECT1FROM pg_rewriteWHERE ev_class=c.oidAND ev_type='3'AND is_instead))
1897+
CAST(CASE WHENc.relkind='r'OR
1898+
(c.relkind='v'AND pg_view_is_insertable(c.oid))
19021899
THEN'YES' ELSE'NO' ENDAS yes_or_no)AS is_insertable_into,
19031900

19041901
CAST(CASE WHENt.typnameIS NOT NULL THEN'YES' ELSE'NO' ENDAS yes_or_no)AS is_typed,
@@ -2497,14 +2494,11 @@ CREATE VIEW views AS
24972494
CAST('NONE'AS character_data)AS check_option,
24982495

24992496
CAST(
2500-
CASE WHEN EXISTS (SELECT1FROM pg_rewriteWHERE ev_class=c.oidAND ev_type='2'AND is_instead)
2501-
AND EXISTS (SELECT1FROM pg_rewriteWHERE ev_class=c.oidAND ev_type='4'AND is_instead)
2502-
THEN'YES' ELSE'NO' END
2497+
CASE WHEN pg_view_is_updatable(c.oid) THEN'YES' ELSE'NO' END
25032498
AS yes_or_no)AS is_updatable,
25042499

25052500
CAST(
2506-
CASE WHEN EXISTS (SELECT1FROM pg_rewriteWHERE ev_class=c.oidAND ev_type='3'AND is_instead)
2507-
THEN'YES' ELSE'NO' END
2501+
CASE WHEN pg_view_is_insertable(c.oid) THEN'YES' ELSE'NO' END
25082502
AS yes_or_no)AS is_insertable_into,
25092503

25102504
CAST(

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