user: Question: Who directed the episode that had 12.88 million viewers?
Columns: ['No. in series', 'Title', 'Directed by', 'Written by', 'Original air date', 'U.S. viewers (million)']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, '"Pilot"', 'Charles McDougall', 'Robert King & Michelle King', 'September22,2009', '13.71']
SQL:

assistant: SELECT "Directed by" FROM "Table" WHERE "U.S. viewers (million)" = '12.88';