diff options
Diffstat (limited to 'doc/src/sgml/ref/create_rule.sgml')
| -rw-r--r-- | doc/src/sgml/ref/create_rule.sgml | 25 |
1 files changed, 19 insertions, 6 deletions
diff --git a/doc/src/sgml/ref/create_rule.sgml b/doc/src/sgml/ref/create_rule.sgml index d4c3392129..381ea3ed6b 100644 --- a/doc/src/sgml/ref/create_rule.sgml +++ b/doc/src/sgml/ref/create_rule.sgml @@ -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> |