Thread: SQL function triggers

I would like to write a function as a set of SQL statements, and then 
use that function
in a trigger. However, since triggers require a return type of opaque, 
and SQL functions
cannot return type opaque, this doesn't look possible. Am I missing 
something? The SQL
that I would expect to do this is below. Incidentally, on an insert, 
would the trigger fire
once, twice, or infinitely?

create table test(
a integer,
b integer
) without oids;

create function test_func( test.a%TYPE )
RETURNS ?????
AS
'update test set b = a where a = $1;'
language SQL
with (isstrict);

create trigger test_trig after update
on test for each row
execute procedure test_func( a );

Brian Blaha <bblaha@umr.edu> writes:
> I would like to write a function as a set of SQL statements, and then 
> use that function
> in a trigger. However, since triggers require a return type of opaque, 
> and SQL functions
> cannot return type opaque, this doesn't look possible.

You could call a SQL function from a trigger, but it can't be a trigger
itself; at present triggers have to be in C, plpgsql, or pltcl (maybe
plpython?  Not sure about that one).

For what you are doing (transferring info from one table to another)
I suspect a rule might work better than a trigger anyway.
        regards, tom lane

Brian Blaha wrote:
> 
> I would like to write a function as a set of SQL statements, and then
> use that function
> in a trigger. However, since triggers require a return type of opaque,
> and SQL functions
> cannot return type opaque, this doesn't look possible. Am I missing
> something? The SQL
> that I would expect to do this is below. Incidentally, on an insert,
> would the trigger fire
> once, twice, or infinitely?
> 
> create table test(
> a integer,
> b integer
> ) without oids;
> 
> create function test_func( test.a%TYPE )
> RETURNS ?????
> AS
> 'update test set b = a where a = $1;'
> language SQL
> with (isstrict);
> 
> create trigger test_trig after update
> on test for each row
> execute procedure test_func( a );

If you intend to modify the updated row only with information available
in the row itself (as in your example), a BEFORE trigger in PL/pgSQL
modifying and returning NEW should get the job done.


Jan

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