newbie question - delete before insert

Grant Mckenzie wrote on 20.11.2010 07:00:

How do people implement insert or upate ( otherwise known as upsert )
behaviour in postgres i.e. insert a row if it's key does not exist in
the database else update the existing row?

You can simply send the UPDATE, if nothing was updated, it's safe to send the INSERT

Regards
Thomas

On 11/20/2010 02:43 PM, Thomas Kellerer wrote:

Grant Mckenzie wrote on 20.11.2010 07:00:

How do people implement insert or upate ( otherwise known as upsert )
behaviour in postgres i.e. insert a row if it's key does not exist in
the database else update the existing row?

You can simply send the UPDATE, if nothing was updated, it's safe to
send the INSERT

Regards
Thomas

something on the line of ....

http://www.postgresql.org/docs/8.4/interactive/plpgsql-control-structures.html

*Example 38-2. Exceptions with UPDATE/INSERT*

--

With Regards
Ashish Karalkar

How do people implement insert or upate ( otherwise known as upsert ) behaviour in postgres i.e. insert a row if it's key does not exist in the database else update the existing row?

I tried using an insert rule to delete any existing rows first then insert however this leads to infinitely recursive rules ( which postgres properly rejects. )

I'm guesisng that the most sensible approach would be a stored proc/function?

I've done it with an on insert trigger. The where clause contains the
values that make this row unique. If it finds another row with the same
fields, it doe san update instead of the insert:

CREATE OR REPLACE FUNCTION stock.trg_beforeinsertstock()
RETURNS "trigger" AS
$BODY$
declare
v_stockid int;
begin
select stockid into v_stockid from stock where pnid=new.pnid
and ownerid=new.ownerid and
coalesce(stocklocationid,-1)=coalesce(new.stocklocationid,-1)
and coalesce(batchid,-1)=coalesce(new.batchid,-1);
if v_stockid is not null then
Update stock set stock=stock+new.stock where stockid=v_stockid;
return null;
else
return new;
end if;
end;
$BODY$
LANGUAGE plpgsql VOLATILE;