user: Question: who are the directors of the episode that had 20.5 millions of north american viewers? 
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code(s)', 'U.S. viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: [122.0, 1.0, '" The One After Vegas "', 'Kevin S. Bright', 'Adam Chase', 'September23,1999', 225551.0, '27.7']
SQL:

assistant: SELECT "Directed by" FROM "Table" WHERE "U.S. viewers (millions)" = '20.5';