ORA-12013 on Fast Refreshable view

Question

Hi,
I'am trying to create an update mview but encoutering ORA-12013.
The problem is , if i comment for update clause in the create statment, the mview is correctly created :
create materialized view AGREGAT_MVNO_RC
build deferred
refresh
fast
on demand
with primary key
for update
enable query rewrite
as
SELECT
LIBELLE_MVNO,
PTA_ID,
TYPE_USAGE,
CODE_CHARGE,
TRUNC( DATE_DEBUT_PERIODE, 'MM') AS MOIS_DATE_DEBUT,
TRUNC( DATE_VALORISATION, 'MM') AS MOIS_VALORISATION,
SUM( MONTANT) AS MONTANT, COUNT( MONTANT) AS NB_MONTANT,
COUNT( *) AS NB_ENR
FROM
CHARGE_VALORISEE_RC
GROUP BY
LIBELLE_MVNO,
PTA_ID,
TYPE_USAGE,
CODE_CHARGE,
TRUNC( DATE_DEBUT_PERIODE, 'MM'),
TRUNC( DATE_VALORISATION, 'MM');
=>produce ORA-12013
create materialized view AGREGAT_MVNO_RC
build deferred
refresh
fast
on demand
with primary key
--for update
enable query rewrite
as
SELECT
LIBELLE_MVNO,
PTA_ID,
TYPE_USAGE,
CODE_CHARGE,
TRUNC( DATE_DEBUT_PERIODE, 'MM') AS MOIS_DATE_DEBUT,
TRUNC( DATE_VALORISATION, 'MM') AS MOIS_VALORISATION,
SUM( MONTANT) AS MONTANT, COUNT( MONTANT) AS NB_MONTANT,
COUNT( *) AS NB_ENR
FROM
CHARGE_VALORISEE_RC
GROUP BY
LIBELLE_MVNO,
PTA_ID,
TYPE_USAGE,
CODE_CHARGE,
TRUNC( DATE_DEBUT_PERIODE, 'MM'),
TRUNC( DATE_VALORISATION, 'MM');
=> No errors
i don't understand why ?
Evironment: 10.2.0.3 enterprise on hp-ux
Thanks for help

Answer 1

The error message description seems clear enough :
ORA-12013 : updatable materialized views must be simple enough to do fast refresh
Cause: The updatable materialized view query contained a join, subquery, union, connect by, order by, or group by caluse.
Action: Make the materialized view simpler. If a join is really needed, make multiple simple materialized views then put a view on top of them.
Nicolas.