user: Question:  how many airport with rank being 4
Columns: ['Rank', 'Airport', 'Total Passengers', '% Change 2005/2006', 'International Passengers', 'Domestic Passengers', 'Transit Passengers', 'Aircraft Movements', 'Freight (Metric Tonnes)']
Types: ['real', 'text', 'real', 'text', 'real', 'real', 'real', 'real', 'real']
Sample row: [1.0, 'London Heathrow', 67527923.0, '0.6%', 61345841.0, 5993386.0, 188696.0, 477048.0, 1263128.0]
SQL:

assistant: SELECT COUNT("Airport") FROM "Table" WHERE "Rank" = 4.0;