Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_13638 ( "Stage" text, "Winner" text, "General classification" text, "Points classification" text, "Mountains classification" text, "Young rider classification" text )

### Question ###
What's the mountains classification when the points classification is Alessandro Petacchi and the general classification is Danilo Di Luca?

### Accurate SQL ###

SELECT "Mountains classification" FROM table_13638 WHERE "Points classification" = 'alessandro petacchi' AND "General classification" = 'danilo di luca'