Hello , (google translate) I am a little fun with the optimizer . sql>s elec t count (distinct idvisiteur ) from src_inbox__at__lm__visites ; + ---------- + | L1 | + + ========== | 75528080 | + ---------- + 1 tuple ( 3m 51s ) sql> set optimizer = ' minimal_pipe ; sql> select count (distinct idvisiteur ) from src_inbox__at__lm__visites ; + ---------- + | L1 | + + ========== | 75528080 | + ---------- + 1 tuple (1m 28s ) sql> set optimizer = ' default_pipe ; sql> select count (distinct idvisiteur ) from src_inbox__at__lm__visites ; + ---------- + | L1 | + + ========== | 75528080 | + ---------- + 1 tuple ( 3m 54s ) It's very interesting . Is there a risk to change optimizer ? What are the best practices ? thank you -- 1G6 52 route de bischwiller 67300 Schiltigheim Société de Services et de Formations en Logiciels Libres http://1g6.biz Tél : 06 64 63 70 35