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Small wording improvement and clarification in PL/pgSQL trigger documentation

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Peter Eisentraut 2009-12-28 19:11:51 +00:00
parent 0d399d57d5
commit 50ef9f7b06
1 changed files with 18 additions and 8 deletions
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doc/src/sgml/plpgsql.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.148 2009/12/19 01:49:02 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/plpgsql.sgml,v 1.149 2009/12/28 19:11:51 petere Exp $ -->
<chapter id="plpgsql">
<title><application>PL/pgSQL</application> - <acronym>SQL</acronym> Procedural Language</title>
@ -3197,16 +3197,26 @@ RAISE unique_violation USING MESSAGE = 'Duplicate user ID: ' || user_id;
for this row). If a nonnull
value is returned then the operation proceeds with that row value.
Returning a row value different from the original value
of <varname>NEW</> alters the row that will be inserted or updated
(but has no direct effect in the <command>DELETE</> case).
To alter the row to be stored, it is possible to replace single values
directly in <varname>NEW</> and return the modified <varname>NEW</>,
or to build a complete new record/row to return.
of <varname>NEW</> alters the row that will be inserted or
updated. Thus, if the trigger function wants the triggering
action to succeed normally without altering the row
value, <varname>NEW</varname> (or a value equal thereto) has to be
returned. To alter the row to be stored, it is possible to
replace single values directly in <varname>NEW</> and return the
modified <varname>NEW</>, or to build a complete new record/row to
return. In the case of a before-trigger
on <command>DELETE</command>, the returned value has no direct
effect, but it has to be nonnull to allow the trigger action to
proceed. Note that <varname>NEW</varname> is null
in <command>DELETE</command> triggers, so returning that is
usually not sensible. A useful idiom in <command>DELETE</command>
triggers might be to return <varname>OLD</varname>.
</para>
<para>
The return value of a <literal>BEFORE</> or <literal>AFTER</>
statement-level trigger or an <literal>AFTER</> row-level trigger is
The return value of a row-level trigger
fired <literal>AFTER</literal> or a statement-level trigger
fired <literal>BEFORE</> or <literal>AFTER</> is
always ignored; it might as well be null. However, any of these types of
triggers might still abort the entire operation by raising an error.
</para>