user: Question: What is the total number of production code listings of episodes written by Matthew Lau?
Columns: ['No. in series', 'No. in season', 'Title', 'Directed by', 'Written by', 'Original air date', 'Production code', 'U.S. viewers (million)']
Types: ['real', 'real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [14.0, 1.0, '" Chuck Versus the First Date "', 'Jason Ensler', 'Josh Schwartz & Chris Fedak', 'September29,2008', '3T7251', '6.84']
SQL:

assistant: SELECT COUNT("Production code") FROM "Table" WHERE "Written by" = 'Matthew Lau';