user: Question: What's the season number of the episode originally seen by 6.64 million people in the US?
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [24.0, 1.0, '"Camp Refoogee"', 'Albert Calleros', 'Josh Bycel & Jonathan Fener', 'September10,2006', '2AJN06', '8.93']
SQL:

assistant: SELECT "No. in season" FROM "Table" WHERE "U.S. viewers (millions)" = '6.64';