CREATE TABLE table_15088557_1 (stage NUMBER, mountains_classification VARCHAR2, winner VARCHAR2)

what is the minimum stage where mountains classification is aitor osa and aitor gonz lez won?
SELECT MIN(stage) FROM table_15088557_1 WHERE mountains_classification = "Aitor Osa" AND winner = "Aitor González"
SELECT MIN("stage") FROM "table_15088557_1" WHERE "Aitor González" = "winner" AND "Aitor Osa" = "mountains_classification"