Re: Getting one row for each subquery row...?

First off, I've nerver heard of using Floating point for money. There
**IS** rounding and truncation that goes on, in even double precision.
The bean counters get upset if you lose .0000001 dollars, especially if
it occurs for several million transactions. The usual choice is DECIMAL.

And I'd use some sort of DATE or TIMESTAMP for the date. and time values.

since you didn't supply any notes, it would be easier to understand if
you used foreign key constraints, and a sounder design perhaps.

And so that I can understand my own queries, I indent them etc(postgres
cares not):

select
    t_stockchanges.productid,
    (select
        name from t_productgroups
    where id=
        (select
           productgroupid from t_prod_in_pgr
        where productid=t_stockchanges.productid
        )
    )
as pgroup
from t_stockchanges;

From you table definitions and titles, I assume, 't_prod_in_pgr' is 'product in process'. You are making an assumption
thata user (?) web user (?) can only have on line entered in that table at a time? 

You will have to explain more about this for me to get it, perhaps for others you will not.

Also, it seems to me that 'productgroupid' should be related to 't_productgroups', but I can not tell.

Tell us more, it gets 'curiouser and curiouser'!