Question: When 19 is the stage who is the points classification?
SQL: SELECT "Points classification" FROM "1-18733814-2" WHERE "Stage" = 19.0;

Question: When Thomas Löfkvist is the  young rider classification and Alessandro Petacchi is the points classification who are the general classifications? 
SQL: SELECT "General classification" FROM "1-18733814-2" WHERE "Points classification" = 'Alessandro Petacchi' AND "Young rider classification" = 'Thomas Löfkvist';

Question: When  Thomas Löfkvist is the general classification who is the winner?
SQL: SELECT "Winner" FROM "1-18733814-2" WHERE "General classification" = 'Thomas Löfkvist';

Question: When Philippe Gilbert is the winner who is the points classification?
SQL: SELECT "Points classification" FROM "1-18733814-2" WHERE "Winner" = 'Philippe Gilbert';

Question: When Danilo Di Luca is the winner who is the general classification? 
SQL: SELECT "General classification" FROM "1-18733814-2" WHERE "Winner" = 'Danilo Di Luca';