Re: Number of updated rows with LibPQ

On Wed, Oct 5, 2022 at 8:17 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Laurenz Albe <laurenz.albe@cybertec.at> writes:
> > On Wed, 2022-10-05 at 16:38 +0200, Dominique Devienne wrote:
> > Yes, you have to use PQcmdTuples(), and you have to convert the string to an integer.
> > But don't worry: the result will *not* be "INSERT 0 5", it will be just "5"

Thanks. What's the leading 0 though, then?
I guessed it might be the number of rows returned, but it isn't, see below:

postgres=# create table foo (id serial primary key, v int);
CREATE TABLE
postgres=# insert into foo (v) values (1), (2) returning id;
 id
----
  1
  2
(2 rows)

INSERT 0 2

> Yeah, just applying atoi() or atol() to the result should be enough.

Thanks too. Since I'm in C++, I used <charconv> instead, and
discovered it can be empty something, not 0.
I guess atoi() would have hidden that distinction, and worked anyway
(returning 0).

In the same topic, I've noticed an INSERT returns PGRES_COMMAND_OK,
while an INSERT-RETURNING returns PGRES_TUPLES_OK. So there's no way
to use the status to distinguish a SELECT from anything else? A RETURNING clause
makes any statement supporting it an hybrid of a command and a query,
but then how
does one know the exact "kind" of the statement?

E.g. So how does psql show INSERT in either cases? By parsing the SQL
itself, client-side?
Or is there a libpq API on PGresult that would allow to get the type
of statement the result is from?

Thanks, --DD