user: Question: How many directors got 6.79 million U.S. viewers from their episodes?
Columns: ['No. in series', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (million)']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, '" Pilot "', 'Julie Anne Robinson', 'DeAnn Heline & Eileen Heisler', 'September30,2009', '276047', '8.71']
SQL:

assistant: SELECT COUNT("Directed by") FROM "Table" WHERE "U.S. viewers (million)" = '6.79';