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RedHat 9 (Linux i386) - man page for create_trigger (redhat section 7)

CREATE TRIGGER(7)			   SQL Commands 			CREATE TRIGGER(7)

NAME
       CREATE TRIGGER - define a new trigger

SYNOPSIS
       CREATE TRIGGER name { BEFORE | AFTER } { event [OR ...] }
	   ON table FOR EACH { ROW | STATEMENT }
	   EXECUTE PROCEDURE func ( arguments )

   INPUTS
       name   The  name to give the new trigger. This must be distinct from the name of any other
	      trigger for the same table.

       event  One of INSERT, DELETE or UPDATE.

       table  The name (optionally schema-qualified) of the table the trigger is for.

       func   A user-supplied function that is declared as taking no arguments and returning type
	      trigger.

       arguments
	      An  optional  comma-separated list of arguments to be provided to the function when
	      the trigger is executed, along with the standard trigger data such as old  and  new
	      tuple  contents.	The  arguments	are  literal  string  constants. Simple names and
	      numeric constants may be written here too,  but  they  will  all	be  converted  to
	      strings.

   OUTPUTS
       CREATE TRIGGER
	      This message is returned if the trigger is successfully created.

DESCRIPTION
       CREATE  TRIGGER	will  enter a new trigger into the current data base. The trigger will be
       associated with the relation table and will execute the specified function func.

       The trigger can be specified to fire either before BEFORE the operation is attempted on	a
       tuple  (before  constraints  are checked and the INSERT, UPDATE or DELETE is attempted) or
       AFTER the operation has been attempted  (e.g.,  after  constraints  are	checked  and  the
       INSERT,	UPDATE or DELETE has completed). If the trigger fires before the event, the trig-
       ger may skip the operation for the current tuple, or change the tuple being inserted  (for
       INSERT  and  UPDATE  operations	only). If the trigger fires after the event, all changes,
       including the last insertion, update, or deletion, are ``visible'' to the trigger.

       If multiple triggers of the same kind are defined for the same event, they will	be  fired
       in alphabetical order by name.

       SELECT does not modify any rows so you can not create SELECT triggers. Rules and views are
       more appropriate in such cases.

       Refer to the chapters on SPI and Triggers in the PostgreSQL Programmer's  Guide	for  more
       information.

NOTES
       To create a trigger on a table, the user must have the TRIGGER privilege on the table.

       In  PostgreSQL  versions  before  7.3,  it  was	necessary to declare trigger functions as
       returning the placeholder type opaque, rather than trigger. To support loading of old dump
       files,  CREATE  TRIGGER	will  accept a function declared as returning opaque, but it will
       issue a NOTICE and change the function's declared return type to trigger.

       As of the current release, STATEMENT triggers are not implemented.

       Refer to the DROP TRIGGER [drop_trigger(7)] command for information on how to remove trig-
       gers.

EXAMPLES
       Check  if the specified distributor code exists in the distributors table before appending
       or updating a row in the table films:

       CREATE TRIGGER if_dist_exists
	   BEFORE INSERT OR UPDATE ON films FOR EACH ROW
	   EXECUTE PROCEDURE check_primary_key ('did', 'distributors', 'did');

       Before cancelling a distributor or updating its code, remove every reference to the  table
       films:

       CREATE TRIGGER if_film_exists
	   BEFORE DELETE OR UPDATE ON distributors FOR EACH ROW
	   EXECUTE PROCEDURE check_foreign_key (1, 'CASCADE', 'did', 'films', 'did');

       The second example can also be done by using a foreign key, constraint as in:

       CREATE TABLE distributors (
	   did	    DECIMAL(3),
	   name     VARCHAR(40),
	   CONSTRAINT if_film_exists
	   FOREIGN KEY(did) REFERENCES films
	   ON UPDATE CASCADE ON DELETE CASCADE
       );

COMPATIBILITY
       SQL92  There is no CREATE TRIGGER statement in SQL92.

       SQL99  The  CREATE  TRIGGER statement in PostgreSQL implements a subset of the SQL99 stan-
	      dard. The following functionality is missing:

	      o SQL99 allows triggers to fire on updates to specific columns (e.g., AFTER  UPDATE
		OF col1, col2).

	      o SQL99 allows you to define aliases for the ``old'' and ``new'' rows or tables for
		use in the definition of the triggered action (e.g., CREATE TRIGGER ... ON table-
		name  REFERENCING OLD ROW AS somename NEW ROW AS othername ...). Since PostgreSQL
		allows trigger procedures to be written in any number of user-defined  languages,
		access to the data is handled in a language-specific way.

	      o PostgreSQL only has row-level triggers, no statement-level triggers.

	      o PostgreSQL  only  allows  the  execution  of a stored procedure for the triggered
		action.  SQL99 allows the execution of a number of other SQL  commands,  such  as
		CREATE	TABLE as triggered action.  This limitation is not hard to work around by
		creating a stored procedure that executes these commands.

       SQL99 specifies that multiple triggers should be fired in  time-of-creation  order.  Post-
       greSQL uses name order, which was judged more convenient to work with.

SEE ALSO
       CREATE  FUNCTION  [create_function(7)],	ALTER  TRIGGER	[alter_trigger(l)],  DROP TRIGGER
       [drop_trigger(l)], PostgreSQL Programmer's Guide

SQL - Language Statements		    2002-11-22				CREATE TRIGGER(7)


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