PostgreSQL server does not increment a SERIAL internally

Hello,

Me and my team passed a full weekend hunting a bug in our Perl written
software were rows have been inserted with the same id 'acq_haushalt.hnr'
which should not have been the case because any budget year in that
table has a single internal number 'hnr'

The table in the 11.4 server is created as:

create table acq_haushalt (
hnr serial not NULL , /* internal budget year number primary key */
hjahr smallint not NULL , /* budget year */
stufe smallint not NULL , /* level 0,1,2,3 */
kurzname char (16) , /* short name for ... */
...
);

We update the serial 'acq_haushalt_hnr_seq' with this statement after loading:

/* table: acq_haushalt */
DO $$
DECLARE
max_id int;
BEGIN
if to_regclass('acq_haushalt') is not null then
SELECT INTO max_id GREATEST(COALESCE(max(hnr), 0),0) + 1 FROM acq_haushalt;
RAISE NOTICE '% % %', 'acq_haushalt', 'hnr', max_id ;
EXECUTE 'ALTER SEQUENCE acq_haushalt_hnr_seq RESTART ' || max_id::text;
end if;
END $$ LANGUAGE plpgsql;

Usage in Perl DBI to get the next value for acq_haushalt.hnr:

if ( &getDBDriverName eq 'Pg') {
$erg = &selectData("SELECT NEXTVAL('acq_haushalt_hnr_seq')",[]);
if ($erg->{'CountData'} == 0) {
$newhnr=1;
}else{
$newhnr=$erg->{'Data'}->[0]->{$erg->{'Fields'}->[0]->{'Name'}};
}
} else { .... code block for Sybase ...

}

But the serial was not incremented internally as we could see with
'psql' and so more than one row was build and inserted with the same
number in $newhnr.

What helped was using:

$erg = &selectData("SELECT max(hnr) FROM acq_haushalt",[]);
if ($erg->{'CountData'} == 0) {
$newhnr=1;
}else{
$newhnr=$erg->{'Data'}->[0]->{$erg->{'Fields'}->[0]->{'Name'}}+1;
}

What we are doing wrong?

Thanks

matthias
--
Matthias Apitz, ✉ guru(at)unixarea(dot)de, http://www.unixarea.de/ +49-176-38902045
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