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Support automatically-updatable views.

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This patch makes "simple" views automatically updatable, without the need
to create either INSTEAD OF triggers or INSTEAD rules.  "Simple" views
are those classified as updatable according to SQL-92 rules.  The rewriter
transforms INSERT/UPDATE/DELETE commands on such views directly into an
equivalent command on the underlying table, which will generally have
noticeably better performance than is possible with either triggers or
user-written rules.  A view that has INSTEAD OF triggers or INSTEAD rules
continues 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 be
added in future.

Dean Rasheed, reviewed by Amit Kapila
This commit is contained in:
Tom Lane
2012-12-08 18:25:48 -05:00
parent d12d9f595e
commit a99c42f291
20 changed files with 2492 additions and 94 deletions
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25
doc/src/sgml/ref/create_rule.sgml
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@@ -45,10 +45,10 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
additional commands to be executed when a given command on a given
table is executed. Alternatively, an <literal>INSTEAD</literal>
rule can replace a given command by another, or cause a command
not to be executed at all. Rules are used to implement table
not to be executed at all. Rules are used to implement SQL
views as well. It is important to realize that a rule is really
a command transformation mechanism, or command macro. The
transformation happens before the execution of the commands starts.
transformation happens before the execution of the command starts.
If you actually want an operation that fires independently for each
physical row, you probably want to use a trigger, not a rule.
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
sufficient for your purposes) to replace update actions on the view
with appropriate updates on other tables. If you want to support
<command>INSERT RETURNING</> and so on, then be sure to put a suitable
<literal>RETURNING</> clause into each of these rules. Alternatively,
an updatable view can be implemented using <literal>INSTEAD OF</>
triggers (see <xref linkend="sql-createtrigger">).
<literal>RETURNING</> clause into each of these rules.
</para>
<para>
There is a catch if you try to use conditional rules for view
There is a catch if you try to use conditional rules for complex view
updates: there <emphasis>must</> be an unconditional
<literal>INSTEAD</literal> rule for each action you wish to allow
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
<literal>INSTEAD NOTHING</literal> action. (This method does not
currently work to support <literal>RETURNING</> queries, however.)
</para>
<note>
<para>
A view that is simple enough to be automatically updatable (see <xref
linkend="sql-createview">) does not require a user-created rule in
order to be updatable. While you can create an explicit rule anyway,
the automatic update transformation will generally outperform an
explicit rule.
</para>
<para>
Another alternative worth considering is to use <literal>INSTEAD OF</>
triggers (see <xref linkend="sql-createtrigger">) in place of rules.
</para>
</note>
</refsect1>
<refsect1>