user: Question: How many production codes were in series 39?
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'real']
Sample row: [23.0, 1.0, '"Rachel\'s Place"', 'Richard Correll', 'David W. Duclon & Gary Menteer', 'September 21, 1990', 446451.0]
SQL:

assistant: SELECT COUNT("Production code") FROM "Table" WHERE "No. in series" = 39.0;