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Commit3f9fe9b

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Doc: update CREATE RULE ref page's hoary discussion of views.
This text left one with the impression that an ON SELECT rule couldbe attached to a plain table, which has not been true since commit264c068 (meaning the text was already misleading when written,evidently by me in96bd67f). However, it didn't get really baduntilb23cd18 removed the convert-a-table-to-a-view logic, whichhad made it possible for scripts that thought they were attachingON SELECTs to tables to still work.Rewrite into a form that makes it clear that an ON SELECT ruleis better regarded as an implementation detail of a view.Pre-v16, point out that adding ON SELECT to a table actuallyconverts it to a view.Per bug #18178 from Joshua Uyehara. Back-patch to all supportedbranches.Discussion:https://postgr.es/m/18178-05534d7064044d2d@postgresql.org
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‎doc/src/sgml/ref/create_rule.sgml

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@@ -59,15 +59,17 @@ CREATE [ OR REPLACE ] RULE <replaceable class="parameter">name</replaceable> AS
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</para>
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<para>
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Presently, <literal>ON SELECT</literal> rules must be unconditional
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<literal>INSTEAD</literal> rules and must have actions that consist
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of a single <command>SELECT</command> command. Thus, an
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<literal>ON SELECT</literal> rule effectively turns the table into
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a view, whose visible contents are the rows returned by the rule's
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<command>SELECT</command> command rather than whatever had been
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stored in the table (if anything). It is considered better style
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to write a <command>CREATE VIEW</command> command than to create a
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real table and define an <literal>ON SELECT</literal> rule for it.
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Presently, <literal>ON SELECT</literal> rules can only be attached
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to views. (Attaching one to a table converts the table into a view.)
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Such a rule must be named <literal>"_RETURN"</literal>,
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must be an unconditional <literal>INSTEAD</literal> rule, and must have
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an action that consists of a single <command>SELECT</command> command.
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This command defines the visible contents of the view. (The view
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itself is basically a dummy table with no storage.) It's best to
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regard such a rule as an implementation detail. While a view can be
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redefined via <literal>CREATE OR REPLACE RULE "_RETURN" AS
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...</literal>, it's better style to use <literal>CREATE OR REPLACE
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VIEW</literal>.
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</para>
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<para>

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