user: Question: How many writers write the episode whose director is Jonathan Herron?
Columns: ['Season no.', 'Series no.', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. Viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: [1.0, 156.0, '"Playing Dead"', 'Michael Smith', 'Antoinette Stella', 'April19,2009', 8009.0, '4.57']
SQL:

assistant: SELECT COUNT("Written by") FROM "Table" WHERE "Directed by" = 'Jonathan Herron';