Re: Autoincremental value

adburne(at)asocmedrosario(dot)com(dot)ar writes

> Hi I'm a newbie in postgresql, I came from MSSQL, MySQL and now
> I'm testing postgres.
> In mysql there is a way to make a second autoincrement field, just:
>
> create table table1
> (field1 integer,
> field2 integer autoincrement,
> primary key (field1,field2))
>
> when insert rows:
>
> insert into table1 (field1) values (1);
> insert into table1 (field1) values (1);
> insert into table1 (field1) values (2);
>
> and then select * from table1, you get:
> field1| field2
> ------+-------
> 1 | 1
> 1 | 2
> 2 | 1
> ------+-------
>
> there is a way to do this with postgres???

It looks like a weird feature. Anyway to achieve the same result with
postgresql, a trigger can compute a value for field2 when needed. I believe
this would do:

CREATE OR REPLACE FUNCTION fill_field2() RETURNS trigger AS '
BEGIN
IF new.field2 IS NULL THEN
SELECT 1+coalesce(max(field2),0) INTO new.field2 FROM table1
WHERE field1=new.field1;
END IF;
RETURN new;
END;
' LANGUAGE 'plpgsql';

CREATE TRIGGER insert_table1 BEFORE INSERT on table1 FOR EACH ROW
EXECUTE PROCEDURE fill_field2();

--
Daniel
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