diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/catalogs.sgml | 15 | ||||
| -rw-r--r-- | doc/src/sgml/ref/create_trigger.sgml | 44 | ||||
| -rw-r--r-- | doc/src/sgml/trigger.sgml | 13 |
3 files changed, 50 insertions, 22 deletions
diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml index 487dd7e1690..174dd0ee819 100644 --- a/doc/src/sgml/catalogs.sgml +++ b/doc/src/sgml/catalogs.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.209 2009/10/07 22:14:14 alvherre Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/catalogs.sgml,v 2.210 2009/10/14 22:14:21 tgl Exp $ --> <!-- Documentation of the system catalogs, directed toward PostgreSQL developers --> @@ -4745,8 +4745,9 @@ <row> <entry><structfield>tgattr</structfield></entry> <entry><type>int2vector</type></entry> - <entry></entry> - <entry>Currently unused</entry> + <entry><literal><link linkend="catalog-pg-attribute"><structname>pg_attribute</structname></link>.attnum</literal></entry> + <entry>column numbers, if trigger is column-specific; otherwise an + empty array</entry> </row> <row> @@ -4759,6 +4760,14 @@ </tgroup> </table> + <para> + Currently, column-specific triggering is supported only for + <literal>UPDATE</> events, and so <structfield>tgattr</> is relevant + only for that event type. <structfield>tgtype</structfield> might + contain bits for other event types as well, but those are presumed + to be table-wide regardless of what is in <structfield>tgattr</>. + </para> + <note> <para> When <structfield>tgconstraint</> is nonzero, diff --git a/doc/src/sgml/ref/create_trigger.sgml b/doc/src/sgml/ref/create_trigger.sgml index 38036ee1683..04f681f0308 100644 --- a/doc/src/sgml/ref/create_trigger.sgml +++ b/doc/src/sgml/ref/create_trigger.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/ref/create_trigger.sgml,v 1.50 2009/09/19 10:23:27 petere Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/create_trigger.sgml,v 1.51 2009/10/14 22:14:21 tgl Exp $ PostgreSQL documentation --> @@ -49,7 +49,7 @@ CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTE current row, or change the row being inserted (for <command>INSERT</command> and <command>UPDATE</command> operations only). If the trigger fires after the event, all changes, including - the last insertion, update, or deletion, are <quote>visible</quote> + the effects of other triggers, are <quote>visible</quote> to the trigger. </para> @@ -122,6 +122,16 @@ CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTE this specifies the event that will fire the trigger. Multiple events can be specified using <literal>OR</literal>. </para> + + <para> + For <command>UPDATE</command> triggers, it is possible to + specify a list of columns using this syntax: +<synopsis> +UPDATE OF <replaceable>column_name1</replaceable> [, <replaceable>column_name2</replaceable> ... ] +</synopsis> + The trigger will only fire if at least one of the listed columns + is mentioned as a target of the update. + </para> </listitem> </varlistentry> @@ -169,8 +179,8 @@ CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTE literal string constants. Simple names and numeric constants can be written here, too, but they will all be converted to strings. Please check the description of the implementation - language of the trigger function about how the trigger arguments - are accessible within the function; it might be different from + language of the trigger function to find out how these arguments + can be accessed within the function; it might be different from normal function arguments. </para> </listitem> @@ -192,6 +202,18 @@ CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTE </para> <para> + A column-specific trigger (<literal>FOR UPDATE OF + <replaceable>column_name</replaceable></literal>) will fire when any + of its columns are listed as targets in the <command>UPDATE</> + command's <literal>SET</> list. It is possible for a column's value + to change even when the trigger is not fired, because changes made to the + row's contents by <literal>BEFORE UPDATE</> triggers are not considered. + Conversely, a command such as <literal>UPDATE ... SET x = x ...</> + will fire a trigger on column <literal>x</>, even though the column's + value did not change. + </para> + + <para> In <productname>PostgreSQL</productname> versions before 7.3, it was necessary to declare trigger functions as returning the placeholder type <type>opaque</>, rather than <type>trigger</>. To support loading @@ -220,13 +242,6 @@ CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTE <itemizedlist> <listitem> <para> - SQL allows triggers to fire on updates to specific columns - (e.g., <literal>AFTER UPDATE OF col1, col2</literal>). - </para> - </listitem> - - <listitem> - <para> SQL allows you to define aliases for the <quote>old</quote> and <quote>new</quote> rows or tables for use in the definition of the triggered action (e.g., <literal>CREATE TRIGGER ... ON @@ -264,9 +279,10 @@ CREATE TRIGGER <replaceable class="PARAMETER">name</replaceable> { BEFORE | AFTE The <productname>PostgreSQL</productname> behavior is for <literal>BEFORE DELETE</literal> to always fire before the delete action, even a cascading one. This is considered more consistent. There is also unpredictable - behavior when <literal>BEFORE</literal> triggers modify rows that are later - to be modified by referential actions. This can lead to constraint violations - or stored data that does not honor the referential constraint. + behavior when <literal>BEFORE</literal> triggers modify rows or prevent + updates during an update that is caused by a referential action. This can + lead to constraint violations or stored data that does not honor the + referential constraint. </para> <para> diff --git a/doc/src/sgml/trigger.sgml b/doc/src/sgml/trigger.sgml index 50e5943401b..60977cbd564 100644 --- a/doc/src/sgml/trigger.sgml +++ b/doc/src/sgml/trigger.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/trigger.sgml,v 1.58 2009/08/04 22:04:37 petere Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/trigger.sgml,v 1.59 2009/10/14 22:14:21 tgl Exp $ --> <chapter id="triggers"> <title>Triggers</title> @@ -36,10 +36,13 @@ performed. Triggers can be defined to execute either before or after any <command>INSERT</command>, <command>UPDATE</command>, or <command>DELETE</command> operation, either once per modified row, - or once per <acronym>SQL</acronym> statement. Triggers can also fire - for <command>TRUNCATE</command> statements. If a trigger event occurs, - the trigger's function is called at the appropriate time to handle the - event. + or once per <acronym>SQL</acronym> statement. + <command>UPDATE</command> triggers can moreover be set to fire only if + certain columns are mentioned in the <literal>SET</literal> clause of the + <command>UPDATE</command> statement. + Triggers can also fire for <command>TRUNCATE</command> statements. + If a trigger event occurs, the trigger's function is called at the + appropriate time to handle the event. </para> <para> |