Обсуждение: It is doing my head in

Ok all here is an question for you.

I am running pgsql on a linux 5.1 box.

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postgres=> create table smile (
postgres-> s1 integer,
postgres-> s2 integer );
CREATE
postgres=> insert into smile values ( 1 , 2 );
INSERT 17866 1
postgres=> insert into smile values ( 3 , 4 );
INSERT 17867 1
postgres=> select * from smile
postgres-> ;
s1|s2
--+--1| 23| 4
(2 rows)

postgres=> create function ttt() returns integer 
postgres-> as 'select 4 as result'
postgres-> language 'sql' ;
CREATE
postgres=> select * from smile where s2=ttt() ;
s1|s2
--+--3| 4
(1 row)

postgres=> create trigger trg1 after insert on smile for each row
postgres-> execute procedure ttt() ;
ERROR:  CreateTrigger: function ttt () does not exist
postgres=> \q



So my question is - why does the create trigger function fail when the
function does in
fact exist ?


Andrew

> So my question is - why does the create trigger function fail when the
> function does in
> fact exist ?

    In fact - it does NOT exist!

    First  of  all,  the builtin 'sql' language cannot be used to
    create triggers. This must  be  done  in  C  or  one  of  the
    procedural languages PL/pgSQL and PL/Tcl.

    The  reason  why  the  function  doesn't  exist  is because a
    trigger procedure is a function declared  with  no  arguments
    and  a  return  type  of  OPAQUE.  Except for the C language,
    functions in PostgreSQL can be overloaded. Multiple different
    functions  can  have the same name as long as their arguments
    differ.

    In  reality  trigger  procedures  take  arguments.  They  are
    defined  at  CREATE  TRIGGER  time. And they return one or no
    database row of the table they are actually fired for.

    The documentation how to create triggers is  in  chapters  11
    and 13 of the PostgreSQL programmers manual.


Jan

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