user: Question: What is the average Tie no when the date is Birmingham City?
Columns: ['Tie no', 'Home team', 'Score', 'Away team', 'Date']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'Preston North End', '1–1', 'Charlton Athletic', '9 February 1946']
SQL:

assistant: SELECT AVG("Tie no") FROM "Table" WHERE "Date" = 'Birmingham City';