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><H1
><A
NAME="SQL-CREATETRIGGER"
></A
>CREATE TRIGGER</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN74055"
></A
><H2
>Name</H2
>CREATE TRIGGER&nbsp;--&nbsp;define a new trigger</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN74060"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>CREATE [ CONSTRAINT ] TRIGGER <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
> { BEFORE | AFTER | INSTEAD OF } { <TT
CLASS="REPLACEABLE"
><I
>event</I
></TT
> [ OR ... ] }
    ON <TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
>
    [ FROM <TT
CLASS="REPLACEABLE"
><I
>referenced_table_name</I
></TT
> ]
    [ NOT DEFERRABLE | [ DEFERRABLE ] { INITIALLY IMMEDIATE | INITIALLY DEFERRED } ]
    [ FOR [ EACH ] { ROW | STATEMENT } ]
    [ WHEN ( <TT
CLASS="REPLACEABLE"
><I
>condition</I
></TT
> ) ]
    EXECUTE PROCEDURE <TT
CLASS="REPLACEABLE"
><I
>function_name</I
></TT
> ( <TT
CLASS="REPLACEABLE"
><I
>arguments</I
></TT
> )

<SPAN
CLASS="phrase"
><SPAN
CLASS="PHRASE"
>where <TT
CLASS="REPLACEABLE"
><I
>event</I
></TT
> can be one of:</SPAN
></SPAN
>

    INSERT
    UPDATE [ OF <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
> [, ... ] ]
    DELETE
    TRUNCATE</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN74072"
></A
><H2
>Description</H2
><P
>   <TT
CLASS="COMMAND"
>CREATE TRIGGER</TT
> creates a new trigger.  The
   trigger will be associated with the specified table or view and will
   execute the specified function <TT
CLASS="REPLACEABLE"
><I
>function_name</I
></TT
> when certain events occur.
  </P
><P
>   The trigger can be specified to fire before the
   operation is attempted on a row (before constraints are checked and
   the <TT
CLASS="COMMAND"
>INSERT</TT
>, <TT
CLASS="COMMAND"
>UPDATE</TT
>, or
   <TT
CLASS="COMMAND"
>DELETE</TT
> is attempted); or after the operation has
   completed (after constraints are checked and the
   <TT
CLASS="COMMAND"
>INSERT</TT
>, <TT
CLASS="COMMAND"
>UPDATE</TT
>, or
   <TT
CLASS="COMMAND"
>DELETE</TT
> has completed); or instead of the operation
   (in the case of inserts, updates or deletes on a view).
   If the trigger fires before or instead of the event, the trigger can skip
   the operation for the current row, or change the row being inserted (for
   <TT
CLASS="COMMAND"
>INSERT</TT
> and <TT
CLASS="COMMAND"
>UPDATE</TT
> operations
   only). If the trigger fires after the event, all changes, including
   the effects of other triggers, are <SPAN
CLASS="QUOTE"
>"visible"</SPAN
>
   to the trigger.
  </P
><P
>   A trigger that is marked <TT
CLASS="LITERAL"
>FOR EACH ROW</TT
> is called
   once for every row that the operation modifies. For example, a
   <TT
CLASS="COMMAND"
>DELETE</TT
> that affects 10 rows will cause any
   <TT
CLASS="LITERAL"
>ON DELETE</TT
> triggers on the target relation to be
   called 10 separate times, once for each deleted row. In contrast, a
   trigger that is marked <TT
CLASS="LITERAL"
>FOR EACH STATEMENT</TT
> only
   executes once for any given operation, regardless of how many rows
   it modifies (in particular, an operation that modifies zero rows
   will still result in the execution of any applicable <TT
CLASS="LITERAL"
>FOR
   EACH STATEMENT</TT
> triggers).
  </P
><P
>   Triggers that are specified to fire <TT
CLASS="LITERAL"
>INSTEAD OF</TT
> the trigger
   event must be marked <TT
CLASS="LITERAL"
>FOR EACH ROW</TT
>, and can only be defined
   on views. <TT
CLASS="LITERAL"
>BEFORE</TT
> and <TT
CLASS="LITERAL"
>AFTER</TT
> triggers on a view
   must be marked as <TT
CLASS="LITERAL"
>FOR EACH STATEMENT</TT
>.
  </P
><P
>   In addition, triggers may be defined to fire for
   <TT
CLASS="COMMAND"
>TRUNCATE</TT
>, though only
   <TT
CLASS="LITERAL"
>FOR EACH STATEMENT</TT
>.
  </P
><P
>   The following table summarizes which types of triggers may be used on
   tables and views:
  </P
><DIV
CLASS="INFORMALTABLE"
><P
></P
><A
NAME="SUPPORTED-TRIGGER-TYPES"
></A
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><THEAD
><TR
><TH
>When</TH
><TH
>Event</TH
><TH
>Row-level</TH
><TH
>Statement-level</TH
></TR
></THEAD
><TBODY
><TR
><TD
ROWSPAN="2"
ALIGN="CENTER"
><TT
CLASS="LITERAL"
>BEFORE</TT
></TD
><TD
ALIGN="CENTER"
><TT
CLASS="COMMAND"
>INSERT</TT
>/<TT
CLASS="COMMAND"
>UPDATE</TT
>/<TT
CLASS="COMMAND"
>DELETE</TT
></TD
><TD
ALIGN="CENTER"
>Tables</TD
><TD
ALIGN="CENTER"
>Tables and views</TD
></TR
><TR
><TD
ALIGN="CENTER"
><TT
CLASS="COMMAND"
>TRUNCATE</TT
></TD
><TD
ALIGN="CENTER"
>&mdash;</TD
><TD
ALIGN="CENTER"
>Tables</TD
></TR
><TR
><TD
ROWSPAN="2"
ALIGN="CENTER"
><TT
CLASS="LITERAL"
>AFTER</TT
></TD
><TD
ALIGN="CENTER"
><TT
CLASS="COMMAND"
>INSERT</TT
>/<TT
CLASS="COMMAND"
>UPDATE</TT
>/<TT
CLASS="COMMAND"
>DELETE</TT
></TD
><TD
ALIGN="CENTER"
>Tables</TD
><TD
ALIGN="CENTER"
>Tables and views</TD
></TR
><TR
><TD
ALIGN="CENTER"
><TT
CLASS="COMMAND"
>TRUNCATE</TT
></TD
><TD
ALIGN="CENTER"
>&mdash;</TD
><TD
ALIGN="CENTER"
>Tables</TD
></TR
><TR
><TD
ROWSPAN="2"
ALIGN="CENTER"
><TT
CLASS="LITERAL"
>INSTEAD OF</TT
></TD
><TD
ALIGN="CENTER"
><TT
CLASS="COMMAND"
>INSERT</TT
>/<TT
CLASS="COMMAND"
>UPDATE</TT
>/<TT
CLASS="COMMAND"
>DELETE</TT
></TD
><TD
ALIGN="CENTER"
>Views</TD
><TD
ALIGN="CENTER"
>&mdash;</TD
></TR
><TR
><TD
ALIGN="CENTER"
><TT
CLASS="COMMAND"
>TRUNCATE</TT
></TD
><TD
ALIGN="CENTER"
>&mdash;</TD
><TD
ALIGN="CENTER"
>&mdash;</TD
></TR
></TBODY
></TABLE
><P
></P
></DIV
><P
>   Also, a trigger definition can specify a Boolean <TT
CLASS="LITERAL"
>WHEN</TT
>
   condition, which will be tested to see whether the trigger should
   be fired.  In row-level triggers the <TT
CLASS="LITERAL"
>WHEN</TT
> condition can
   examine the old and/or new values of columns of the row.  Statement-level
   triggers can also have <TT
CLASS="LITERAL"
>WHEN</TT
> conditions, although the feature
   is not so useful for them since the condition cannot refer to any values
   in the table.
  </P
><P
>   If multiple triggers of the same kind are defined for the same event,
   they will be fired in alphabetical order by name.
  </P
><P
>   When the <TT
CLASS="LITERAL"
>CONSTRAINT</TT
> option is specified, this command creates a
   <I
CLASS="FIRSTTERM"
>constraint trigger</I
>.  This is the same as a regular trigger
   except that the timing of the trigger firing can be adjusted using
   <A
HREF="sql-set-constraints.html"
>SET CONSTRAINTS</A
>.
   Constraint triggers must be <TT
CLASS="LITERAL"
>AFTER ROW</TT
> triggers.  They can
   be fired either at the end of the statement causing the triggering event,
   or at the end of the containing transaction; in the latter case they are
   said to be <I
CLASS="FIRSTTERM"
>deferred</I
>.  A pending deferred-trigger firing can
   also be forced to happen immediately by using <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
>.
   Constraint triggers are expected to raise an exception when the constraints
   they implement are violated.
  </P
><P
>   <TT
CLASS="COMMAND"
>SELECT</TT
> does not modify any rows so you cannot
   create <TT
CLASS="COMMAND"
>SELECT</TT
> triggers. Rules and views are more
   appropriate in such cases.
  </P
><P
>   Refer to <A
HREF="triggers.html"
>Chapter 36</A
> for more information about triggers.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN74171"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
></DT
><DD
><P
>      The name to give the new trigger.  This must be distinct from
      the name of any other trigger for the same table.
      The name cannot be schema-qualified &mdash; the trigger inherits the
      schema of its table.  For a constraint trigger, this is also the name to
      use when modifying the trigger's behavior using
      <TT
CLASS="COMMAND"
>SET CONSTRAINTS</TT
>.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>BEFORE</TT
><BR><TT
CLASS="LITERAL"
>AFTER</TT
><BR><TT
CLASS="LITERAL"
>INSTEAD OF</TT
></DT
><DD
><P
>      Determines whether the function is called before, after, or instead of
      the event.  A constraint trigger can only be specified as
      <TT
CLASS="LITERAL"
>AFTER</TT
>.
     </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>event</I
></TT
></DT
><DD
><P
>      One of <TT
CLASS="LITERAL"
>INSERT</TT
>, <TT
CLASS="LITERAL"
>UPDATE</TT
>,
      <TT
CLASS="LITERAL"
>DELETE</TT
>, or <TT
CLASS="LITERAL"
>TRUNCATE</TT
>;
      this specifies the event that will fire the trigger. Multiple
      events can be specified using <TT
CLASS="LITERAL"
>OR</TT
>.
     </P
><P
>      For <TT
CLASS="LITERAL"
>UPDATE</TT
> events, it is possible to
      specify a list of columns using this syntax:
</P><PRE
CLASS="SYNOPSIS"
>UPDATE OF <TT
CLASS="REPLACEABLE"
><I
>column_name1</I
></TT
> [, <TT
CLASS="REPLACEABLE"
><I
>column_name2</I
></TT
> ... ]</PRE
><P>
      The trigger will only fire if at least one of the listed columns
      is mentioned as a target of the <TT
CLASS="COMMAND"
>UPDATE</TT
> command.
     </P
><P
><TT
CLASS="LITERAL"
>INSTEAD OF UPDATE</TT
> events do not support lists of columns.
     </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>table_name</I
></TT
></DT
><DD
><P
>      The name (optionally schema-qualified) of the table or view the trigger
      is for.
     </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>referenced_table_name</I
></TT
></DT
><DD
><P
>      The (possibly schema-qualified) name of another table referenced by the
      constraint.  This option is used for foreign-key constraints and is not
      recommended for general use.  This can only be specified for
      constraint triggers.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>DEFERRABLE</TT
><BR><TT
CLASS="LITERAL"
>NOT DEFERRABLE</TT
><BR><TT
CLASS="LITERAL"
>INITIALLY IMMEDIATE</TT
><BR><TT
CLASS="LITERAL"
>INITIALLY DEFERRED</TT
></DT
><DD
><P
>      The default timing of the trigger.
      See the <A
HREF="sql-createtable.html"
>CREATE TABLE</A
> documentation for details of
      these constraint options.  This can only be specified for constraint
      triggers.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>FOR EACH ROW</TT
><BR><TT
CLASS="LITERAL"
>FOR EACH STATEMENT</TT
></DT
><DD
><P
>      This specifies whether the trigger procedure should be fired
      once for every row affected by the trigger event, or just once
      per SQL statement. If neither is specified, <TT
CLASS="LITERAL"
>FOR EACH
      STATEMENT</TT
> is the default.  Constraint triggers can only
      be specified <TT
CLASS="LITERAL"
>FOR EACH ROW</TT
>.
     </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>condition</I
></TT
></DT
><DD
><P
>      A Boolean expression that determines whether the trigger function
      will actually be executed.  If <TT
CLASS="LITERAL"
>WHEN</TT
> is specified, the
      function will only be called if the <TT
CLASS="REPLACEABLE"
><I
>condition</I
></TT
> returns <TT
CLASS="LITERAL"
>true</TT
>.
      In <TT
CLASS="LITERAL"
>FOR EACH ROW</TT
> triggers, the <TT
CLASS="LITERAL"
>WHEN</TT
>
      condition can refer to columns of the old and/or new row values
      by writing <TT
CLASS="LITERAL"
>OLD.<TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
></TT
> or
      <TT
CLASS="LITERAL"
>NEW.<TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
></TT
> respectively.
      Of course, <TT
CLASS="LITERAL"
>INSERT</TT
> triggers cannot refer to <TT
CLASS="LITERAL"
>OLD</TT
>
      and <TT
CLASS="LITERAL"
>DELETE</TT
> triggers cannot refer to <TT
CLASS="LITERAL"
>NEW</TT
>.
     </P
><P
><TT
CLASS="LITERAL"
>INSTEAD OF</TT
> triggers do not support <TT
CLASS="LITERAL"
>WHEN</TT
>
      conditions.
     </P
><P
>      Currently, <TT
CLASS="LITERAL"
>WHEN</TT
> expressions cannot contain
      subqueries.
     </P
><P
>      Note that for constraint triggers, evaluation of the <TT
CLASS="LITERAL"
>WHEN</TT
>
      condition is not deferred, but occurs immediately after the row update
      operation is performed. If the condition does not evaluate to true then
      the trigger is not queued for deferred execution.
     </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>function_name</I
></TT
></DT
><DD
><P
>      A user-supplied function that is declared as taking no arguments
      and returning type <TT
CLASS="LITERAL"
>trigger</TT
>, which is executed when
      the trigger fires.
     </P
></DD
><DT
><TT
CLASS="REPLACEABLE"
><I
>arguments</I
></TT
></DT
><DD
><P
>      An optional comma-separated list of arguments to be provided to
      the function when the trigger is executed.  The arguments are
      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 to find out how these arguments
      can be accessed within the function; it might be different from
      normal function arguments.
     </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATETRIGGER-NOTES"
></A
><H2
>Notes</H2
><P
>   To create a trigger on a table, the user must have the
   <TT
CLASS="LITERAL"
>TRIGGER</TT
> privilege on the table.  The user must
   also have <TT
CLASS="LITERAL"
>EXECUTE</TT
> privilege on the trigger function.
  </P
><P
>   Use <A
HREF="sql-droptrigger.html"
>DROP TRIGGER</A
> to remove a trigger.
  </P
><P
>   A column-specific trigger (one defined using the <TT
CLASS="LITERAL"
>UPDATE OF
   <TT
CLASS="REPLACEABLE"
><I
>column_name</I
></TT
></TT
> syntax) will fire when any
   of its columns are listed as targets in the <TT
CLASS="COMMAND"
>UPDATE</TT
>
   command's <TT
CLASS="LITERAL"
>SET</TT
> 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 <TT
CLASS="LITERAL"
>BEFORE UPDATE</TT
> triggers are not considered.
   Conversely, a command such as <TT
CLASS="LITERAL"
>UPDATE ... SET x = x ...</TT
>
   will fire a trigger on column <TT
CLASS="LITERAL"
>x</TT
>, even though the column's
   value did not change.
  </P
><P
>   In a <TT
CLASS="LITERAL"
>BEFORE</TT
> trigger, the <TT
CLASS="LITERAL"
>WHEN</TT
> condition is
   evaluated just before the function is or would be executed, so using
   <TT
CLASS="LITERAL"
>WHEN</TT
> is not materially different from testing the same
   condition at the beginning of the trigger function.  Note in particular
   that the <TT
CLASS="LITERAL"
>NEW</TT
> row seen by the condition is the current value,
   as possibly modified by earlier triggers.  Also, a <TT
CLASS="LITERAL"
>BEFORE</TT
>
   trigger's <TT
CLASS="LITERAL"
>WHEN</TT
> condition is not allowed to examine the
   system columns of the <TT
CLASS="LITERAL"
>NEW</TT
> row (such as <TT
CLASS="LITERAL"
>oid</TT
>),
   because those won't have been set yet.
  </P
><P
>   In an <TT
CLASS="LITERAL"
>AFTER</TT
> trigger, the <TT
CLASS="LITERAL"
>WHEN</TT
> condition is
   evaluated just after the row update occurs, and it determines whether an
   event is queued to fire the trigger at the end of statement.  So when an
   <TT
CLASS="LITERAL"
>AFTER</TT
> trigger's <TT
CLASS="LITERAL"
>WHEN</TT
> condition does not return
   true, it is not necessary to queue an event nor to re-fetch the row at end
   of statement.  This can result in significant speedups in statements that
   modify many rows, if the trigger only needs to be fired for a few of the
   rows.
  </P
><P
>   In <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> versions before 7.3, it was
   necessary to declare trigger functions as returning the placeholder
   type <TT
CLASS="TYPE"
>opaque</TT
>, rather than <TT
CLASS="TYPE"
>trigger</TT
>.  To support loading
   of old dump files, <TT
CLASS="COMMAND"
>CREATE TRIGGER</TT
> will accept a function
   declared as returning <TT
CLASS="TYPE"
>opaque</TT
>, but it will issue a notice and
   change the function's declared return type to <TT
CLASS="TYPE"
>trigger</TT
>.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATETRIGGER-EXAMPLES"
></A
><H2
>Examples</H2
><P
>   Execute the function <CODE
CLASS="FUNCTION"
>check_account_update</CODE
> whenever
   a row of the table <TT
CLASS="LITERAL"
>accounts</TT
> is about to be updated:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TRIGGER check_update
    BEFORE UPDATE ON accounts
    FOR EACH ROW
    EXECUTE PROCEDURE check_account_update();</PRE
><P>

   The same, but only execute the function if column <TT
CLASS="LITERAL"
>balance</TT
>
   is specified as a target in the <TT
CLASS="COMMAND"
>UPDATE</TT
> command:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TRIGGER check_update
    BEFORE UPDATE OF balance ON accounts
    FOR EACH ROW
    EXECUTE PROCEDURE check_account_update();</PRE
><P>

   This form only executes the function if column <TT
CLASS="LITERAL"
>balance</TT
>
   has in fact changed value:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TRIGGER check_update
    BEFORE UPDATE ON accounts
    FOR EACH ROW
    WHEN (OLD.balance IS DISTINCT FROM NEW.balance)
    EXECUTE PROCEDURE check_account_update();</PRE
><P>

   Call a function to log updates of <TT
CLASS="LITERAL"
>accounts</TT
>, but only if
   something changed:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TRIGGER log_update
    AFTER UPDATE ON accounts
    FOR EACH ROW
    WHEN (OLD.* IS DISTINCT FROM NEW.*)
    EXECUTE PROCEDURE log_account_update();</PRE
><P>

   Execute the function <CODE
CLASS="FUNCTION"
>view_insert_row</CODE
> for each row to insert
   rows into the tables underlying a view:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TRIGGER view_insert
    INSTEAD OF INSERT ON my_view
    FOR EACH ROW
    EXECUTE PROCEDURE view_insert_row();</PRE
><P>
  </P
><P
>   <A
HREF="trigger-example.html"
>Section 36.4</A
> contains a complete example of a trigger
   function written in C.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="SQL-CREATETRIGGER-COMPATIBILITY"
></A
><H2
>Compatibility</H2
><P
>   The <TT
CLASS="COMMAND"
>CREATE TRIGGER</TT
> statement in
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> implements a subset of the
   <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> standard. The following functionalities are currently
   missing:

   <P
></P
></P><UL
><LI
><P
>      SQL allows you to define aliases for the <SPAN
CLASS="QUOTE"
>"old"</SPAN
>
      and <SPAN
CLASS="QUOTE"
>"new"</SPAN
> rows or tables for use in the definition
      of the triggered action (e.g., <TT
CLASS="LITERAL"
>CREATE TRIGGER ... ON
      tablename REFERENCING OLD ROW AS somename NEW ROW AS othername
      ...</TT
>).  Since <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>
      allows trigger procedures to be written in any number of
      user-defined languages, access to the data is handled in a
      language-specific way.
     </P
></LI
><LI
><P
>      <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> does not allow the old and new
      tables to be referenced in statement-level triggers, i.e., the tables
      that contain all the old and/or new rows, which are referred to by the
      <TT
CLASS="LITERAL"
>OLD TABLE</TT
> and <TT
CLASS="LITERAL"
>NEW TABLE</TT
> clauses in
      the <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
> standard.
     </P
></LI
><LI
><P
><SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> only allows the execution
      of a user-defined function for the triggered action.  The standard
      allows the execution of a number of other SQL commands, such as
      <TT
CLASS="COMMAND"
>CREATE TABLE</TT
>, as the triggered action.  This
      limitation is not hard to work around by creating a user-defined
      function that executes the desired commands.
     </P
></LI
></UL
><P>
  </P
><P
>   SQL specifies that multiple triggers should be fired in
   time-of-creation order.  <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> uses
   name order, which was judged to be more convenient.
  </P
><P
>   SQL specifies that <TT
CLASS="LITERAL"
>BEFORE DELETE</TT
> triggers on cascaded
   deletes fire <SPAN
CLASS="emphasis"
><I
CLASS="EMPHASIS"
>after</I
></SPAN
> the cascaded <TT
CLASS="LITERAL"
>DELETE</TT
> completes.
   The <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> behavior is for <TT
CLASS="LITERAL"
>BEFORE
   DELETE</TT
> to always fire before the delete action, even a cascading
   one.  This is considered more consistent.  There is also nonstandard
   behavior if <TT
CLASS="LITERAL"
>BEFORE</TT
> 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.
  </P
><P
>   The ability to specify multiple actions for a single trigger using
   <TT
CLASS="LITERAL"
>OR</TT
> is a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extension of
   the SQL standard.
  </P
><P
>   The ability to fire triggers for <TT
CLASS="COMMAND"
>TRUNCATE</TT
> is a
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extension of the SQL standard, as is the
   ability to define statement-level triggers on views.
  </P
><P
>   <TT
CLASS="COMMAND"
>CREATE CONSTRAINT TRIGGER</TT
> is a
   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> extension of the <ACRONYM
CLASS="ACRONYM"
>SQL</ACRONYM
>
   standard.
  </P
></DIV
><DIV
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><A
NAME="AEN74370"
></A
><H2
>See Also</H2
><A
HREF="sql-altertrigger.html"
>ALTER TRIGGER</A
>, <A
HREF="sql-droptrigger.html"
>DROP TRIGGER</A
>, <A
HREF="sql-createfunction.html"
>CREATE FUNCTION</A
>, <A
HREF="sql-set-constraints.html"
>SET CONSTRAINTS</A
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