Thread

Antw: Insert with replace?

Gerhard Dieringer <dieringg@eba-haus.de> — 2000-06-02T07:02:12Z

Wampler, Steve wrote:

> ...
> I've got a database that (logically) represents a set of
> items, where each item has a primary key represented by two
> columns (id and name).  If that key isn't in the database,
> I want to insert the item.  If that key is in the database, I want
> to update the item.  I have no need to retain the previous
> values.
> 

You can solve your problem with a trigger and a view, that has the same attributes as your table.
You insert the data into the view, not the table. The trigger first looks, if a row with that primary key is allready in the table and decides, 
if to use update or insert into the table.

example:
create table test_table (
  id   int4 primary key,
  data text);

create view test_view as
  select id, data 
    from test_table;

create function insert_or_update() returns opaque as '
  declare 
    lid int4;
  begin
    select t.id into lid
      from test_table t
      where t.id = new.id;
    if found then
      update test_table
         set data = new.data
       where id = new.id;
    else
      insert into test_table 
      values (new.id, new.data);
    end if;
    return null;
  end;
' language 'plpgsql';


create trigger insert_or_update_trigger 
before insert on test_view
   for each row execute procedure insert_or_update();

Of course this solution has some drawbacks. 
PostgreSQL always returns INSERT 0 0, because the insert into the view is canceled by returning null in the trigger.
But it works.

Test it with two inserts, that do insert

insert into test_view values (1,'one');
insert into test_view values (2,'two');

select * from test_view;

Now an insert that dose an update:

insert into test_view values (1,'ONE');

select * from test_view;

Gerhard