user: Question: What average week has Shea Stadium as the game site, and 1979-12-09 as the date?
Columns: ['Week', 'Date', 'Opponent', 'Result', 'Game site', 'Attendance']
Types: ['real', 'text', 'text', 'text', 'text', 'real']
Sample row: [1.0, '1979-09-02', 'Cleveland Browns', 'L 25–22 ( OT )', 'Shea Stadium', 48472.0]
SQL:

assistant: SELECT AVG("Week") FROM "Table" WHERE "Game site" = 'Shea Stadium' AND "Date" = '1979-12-09';