user: Question: What was the publication date of the photos of Sean Preston Federline that cost $500,000 and were published by People?
Columns: ['Type', 'Person(s)', 'Publisher(s)', 'Publication date', 'Reported price']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Baby photos', 'Knox Leon & Vivienne Marcheline Jolie-Pitt', 'People & Hello!', 'August 2008', '$15,000,000']
SQL:

assistant: SELECT "Publication date" FROM "Table" WHERE "Reported price" = '$500,000' AND "Publisher(s)" = 'People' AND "Person(s)" = 'Sean Preston Federline';