user: Question: Who is the directed by when 2T6404 is the production code?
Columns: ['No.', '#', 'Title', 'Directed by', 'Written by', 'U.S. air date', 'Production code', 'U.S. viewers (million)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [89.0, 1.0, '"Arrival"', 'James Marshall', 'Todd Slavkin & Darren Swimmer', 'September29,2005', '2T6401', '5.90']
SQL:

assistant: SELECT "Directed by" FROM "Table" WHERE "Production code" = '2T6404';