<!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.23 2001/05/27 09:59:27 petere Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_rule.sgml,v 1.24 2001/07/09 23:50:31 tgl Exp $
Postgres documentation
-->
<replaceable class="parameter">action</replaceable> part of the rule is
executed. The <replaceable class="parameter">action</replaceable> is
done instead of the original query if INSTEAD is specified; otherwise
- it is done before the original query is performed.
+ it is done after the original query in the case of ON INSERT, or before
+ the original query in the case of ON UPDATE or ON DELETE.
Within both the <replaceable class="parameter">condition</replaceable>
and <replaceable class="parameter">action</replaceable>, values from
fields in the old instance and/or the new instance are substituted for
+<!-- $Header: /cvsroot/pgsql/doc/src/sgml/rules.sgml,v 1.14 2001/07/09 23:50:32 tgl Exp $ -->
+
<Chapter Id="rules">
<Title>The <ProductName>Postgres</ProductName> Rule System</Title>
for a rule with one action.
</Para>
+<Para>
+ For ON INSERT rules, the original query (if not suppressed by INSTEAD)
+ is done before any actions added by rules. This allows the actions to
+ see the inserted row(s). But for ON UPDATE and ON
+ DELETE rules, the original query is done after the actions added by rules.
+ This ensures that the actions can see the to-be-updated or to-be-deleted
+ rows; otherwise, the actions might do nothing because they find no rows
+ matching their qualifications.
+</Para>
+
<Para>
The parsetrees generated from rule actions are thrown into the
rewrite system again and maybe more rules get applied resulting
or another resultrelation. Otherwise this recursive process will end up in a loop.
There is a compiled in recursion limit of currently 10 iterations.
If after 10 iterations there are still update rules to apply the
- rule system assumes a loop over multiple rule definitions and aborts the
- transaction.
+ rule system assumes a loop over multiple rule definitions and reports
+ an error.
</Para>
<Para>
</Para>
<Para>
- It is important, that the original parsetree is executed last.
- The <ProductName>Postgres</ProductName> "traffic cop" does
- a command counter increment between the execution of the two
- parsetrees so the second one can see changes made by the first.
+ Here we can see why it is important that the original parsetree is
+ executed last.
If the UPDATE would have been executed first, all the rows
are already set to zero, so the logging INSERT
would not find any row where 0 != shoelace_data.sl_avail.
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.96 2001/07/06 13:40:47 wieck Exp $
+ * $Header: /cvsroot/pgsql/src/backend/rewrite/rewriteHandler.c,v 1.97 2001/07/09 23:50:32 tgl Exp $
*
*-------------------------------------------------------------------------
*/
numQueryRewriteInvoked - 1);
}
- instead = FALSE;
+ instead = false;
result = RewriteQuery(parsetree, &instead, &qual_products);
foreach(n, result)
}
/*
- * qual_products are the original query with the negated rule
- * qualification of an instead rule
+ * For INSERTs, the original query is done first; for UPDATE/DELETE, it is
+ * done last. This is needed because update and delete rule actions might
+ * not do anything if they are invoked after the update or delete is
+ * performed. The command counter increment between the query execution
+ * makes the deleted (and maybe the updated) tuples disappear so the scans
+ * for them in the rule actions cannot find them.
*/
- if (qual_products != NIL)
- rewritten = nconc(rewritten, qual_products);
-
- /*
- * The original query is appended last (if no "instead" rule) because
- * update and delete rule actions might not do anything if they are
- * invoked after the update or delete is performed. The command
- * counter increment between the query execution makes the deleted
- * (and maybe the updated) tuples disappear so the scans for them in
- * the rule actions cannot find them.
- */
- if (!instead)
- if (parsetree->commandType == CMD_INSERT)
+ if (parsetree->commandType == CMD_INSERT)
+ {
+ /*
+ * qual_products are the original query with the negated rule
+ * qualification of an INSTEAD rule
+ */
+ if (qual_products != NIL)
+ rewritten = nconc(qual_products, rewritten);
+ /*
+ * Add the unmodified original query, if no INSTEAD rule was seen.
+ */
+ if (!instead)
rewritten = lcons(parsetree, rewritten);
- else
+ }
+ else
+ {
+ /*
+ * qual_products are the original query with the negated rule
+ * qualification of an INSTEAD rule
+ */
+ if (qual_products != NIL)
+ rewritten = nconc(rewritten, qual_products);
+ /*
+ * Add the unmodified original query, if no INSTEAD rule was seen.
+ */
+ if (!instead)
rewritten = lappend(rewritten, parsetree);
+ }
return rewritten;
}
create table rtest_nothn3 (a int4, b text);
create table rtest_nothn4 (a int4, b text);
create rule rtest_nothn_r1 as on insert to rtest_nothn1
- where new.a >= 10 and new.a < 20 do instead (select 1);
+ where new.a >= 10 and new.a < 20 do instead nothing;
create rule rtest_nothn_r2 as on insert to rtest_nothn1
where new.a >= 30 and new.a < 40 do instead nothing;
create rule rtest_nothn_r3 as on insert to rtest_nothn2
rtest_emp | rtest_emp_del | CREATE RULE rtest_emp_del AS ON DELETE TO rtest_emp DO INSERT INTO rtest_emplog (ename, who, "action", newsal, oldsal) VALUES (old.ename, "current_user"(), 'fired '::bpchar, '$0.00'::money, old.salary);
rtest_emp | rtest_emp_ins | CREATE RULE rtest_emp_ins AS ON INSERT TO rtest_emp DO INSERT INTO rtest_emplog (ename, who, "action", newsal, oldsal) VALUES (new.ename, "current_user"(), 'hired '::bpchar, new.salary, '$0.00'::money);
rtest_emp | rtest_emp_upd | CREATE RULE rtest_emp_upd AS ON UPDATE TO rtest_emp WHERE (new.salary <> old.salary) DO INSERT INTO rtest_emplog (ename, who, "action", newsal, oldsal) VALUES (new.ename, "current_user"(), 'honored '::bpchar, new.salary, old.salary);
- rtest_nothn1 | rtest_nothn_r1 | CREATE RULE rtest_nothn_r1 AS ON INSERT TO rtest_nothn1 WHERE ((new.a >= 10) AND (new.a < 20)) DO INSTEAD SELECT 1;
+ rtest_nothn1 | rtest_nothn_r1 | CREATE RULE rtest_nothn_r1 AS ON INSERT TO rtest_nothn1 WHERE ((new.a >= 10) AND (new.a < 20)) DO INSTEAD NOTHING;
rtest_nothn1 | rtest_nothn_r2 | CREATE RULE rtest_nothn_r2 AS ON INSERT TO rtest_nothn1 WHERE ((new.a >= 30) AND (new.a < 40)) DO INSTEAD NOTHING;
rtest_nothn2 | rtest_nothn_r3 | CREATE RULE rtest_nothn_r3 AS ON INSERT TO rtest_nothn2 WHERE (new.a >= 100) DO INSTEAD INSERT INTO rtest_nothn3 (a, b) VALUES (new.a, new.b);
rtest_nothn2 | rtest_nothn_r4 | CREATE RULE rtest_nothn_r4 AS ON INSERT TO rtest_nothn2 DO INSTEAD NOTHING;
create table rtest_nothn4 (a int4, b text);
create rule rtest_nothn_r1 as on insert to rtest_nothn1
- where new.a >= 10 and new.a < 20 do instead (select 1);
+ where new.a >= 10 and new.a < 20 do instead nothing;
create rule rtest_nothn_r2 as on insert to rtest_nothn1
where new.a >= 30 and new.a < 40 do instead nothing;
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