Sam Mason wrote:
> > But for rows, there is no such thing. You can't assign null to a row, it
> > makes no sense and actually causes an error.
>
> What makes you say this? There's no reason I can see that would cause
> row values should be special in this way. Maybe if you could define
> what you mean by "you can't assign null to a row"?
It seems to me that there is something special with rows: in tables, the
values of columns may be null or not, but at the level of the row, there is
no information that would say: this row itself as an object is null.
Anyway, let's try to assign null to a row variable (with 8.4.0):
CREATE TABLE our_table(i int);
CREATE FUNCTION test() returns void as $$
declare
r our_table;
begin
r:=null;
end;
$$ LANGUAGE plpgsql;
SELECT test() yields:
ERROR: cannot assign non-composite value to a row variable
CONTEXT: PL/pgSQL function "test" line 4 at assignment
As a follow-up to the comparison between rows and arrays, note that if we'd
make r an int[], there would be no error.
However, I agree that if we consider that a row is a composite type, then
there is a problem because we sure can insert NULL into a column that is of a
composite type. So the "row cannot be null" line of reasoning holds only so
far as you don't stuff rows into columns :)
Best regards,
--
Daniel
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